Novak Djokovic has become the world's top tennis player since overhauling his diet in 2010. "I observed him playing in the Australian Open," says the Serbian's former nutritionist Dr. Igor Cetojevic. "The commentator repeatedly referred to 'his asthma' and the problems he had breathing."
(CNN) -- The lactic acid builds up, your muscles are screaming, your body temperature sky-rockets -- trying to stay two shots ahead of your opponent proves impossible as your thoughts fragment into near delirium.
Five hours charging around a tennis court can be sheer hell even when you're winning, but if your body is out of balance then it's an even harder challenge.
Sunday's Australian Open finalists Novak Djokovic and Andy Murray once struggled with their fitness, but both have transformed their tennis careers since discovering a diet secret that is battling for acceptance in the world of mainstream sports science.
The benefits of going gluten free have been extolled for years by alternative health practitioners, but they have been brought to wider attention due to the exploits of high-profile stars such as Djokovic, whose wheat intolerance caused the world No. 1 severe breathing problems.
Read: The destiny of family guy Djokovic
"I knew from my experience that asthma was not the boy's problem but rather it was reflecting a symptom of something that was going on with his digestion," says Dr. Igor Cetojevic, who worked with Djokovic for a year up until his Wimbledon triumph in 2011.
"It was his sensitivity to gluten that was compromising his lungs," he adds, citing that in Chinese medicine there's believed to be a relationship between the large intestines and the lungs.
Our diet has changed dramatically in the past century, especially in Western countries. It's a trend that's spreading around the world due to the globalization of commerce, and the food industry in particular.
"I believe one of the problems is over consumption of gluten-containing grains, especially wheat, and the fact that it is genetically different from ancient wheat," says naturopathic physician Hamish Everard.
Cutting out wheat-based foods such as bread and pasta could be the best thing you ever do, says one of his clients, tennis coach Pete McCraw, who has helped develop top players such as Maria Sharapova and Jelena Jankovic.
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"The energy level that you have is something I've never experienced before. You don't ever have that crash, the high and then the low," McCraw told CNN.
"Those periods of the day when you crave carbs or sugar, feeling drowsy at work or in the car or wherever, you don't have that anymore, it's a completely different thing -- it's sustained, you don't have the foods cravings like I used to.
"It's a completely different energy source that your body's operating from. The ability to maintain a lean athletic figure is effortless."
The problem is not just wheat, but also processed dairy and sugars -- all of which we consume more regularly and in higher quantities than ever before.
"The gluten in food produces certain conditions; dairy, especially when produced conventionally, contributes to other factors to the detriment of our health," says Cetojevic, who is trained in both conventional and alternative medicine.
"Generally, milk is for babies. We don't need dairy products as we get older," he adds, and also warned against the intake of processed sugar.
"The change in food production has increased yields to the point of surplus but has not improved the quality of the food we eat. Often it contains traces of pesticides, hormones, preservatives, artificial colors, flavor enhancers and I won't even begin to talk about genetically modified organisms."
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About 18 months ago, McCraw started noticing symptoms of extreme lethargy in young players he was working with.
"They were presenting chronic fatigue symptoms, although they weren't diagnosed in a traditional way, in terms of blood markers -- everything would come back reasonably normal," he said.
"Athletes would be complaining of excessive tiredness, even after light sessions. During a normal daily activity it was fine but then as soon as they began to exercise their blood sugar levels would drop significantly, and that causes concentration-behavior issues, (problems with) focus, emotional control.
Novak Djokovic of Serbia celebrates winning the men's singles final match against Andy Murray of Great Britain at the Australian Open in Melbourne on Sunday, January 27. Djokovic won 6-7 (2), 7-6 (3), 6-3, 6-2.
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"By the normal standards these were healthy teenagers and players in their early 20s, but they weren't healthy."
McCraw, who has held top coaching and development roles in his native Australia, New Zealand, Israel and at the Nick Bollettieri academy, works with players from age grade to elite level.
One of his clients had been seeing Everard to treat his celiac disease -- an autoimmune disorder caused by gluten intolerance that attacks the walls of the small intestine and makes it difficult for the body to absorb and process the nutrients that it requires.
Everard says that while only 1% of people are gluten intolerant, more than half of his clients are sensitive to it -- and 93% of them have seen benefits from eliminating gluten from their diet.
The improvements increase even further when processed sugars such as high-fructose corn syrup are taken out of the equation, says McCraw.
You might think bread and pasta are healthy foods, but essentially they break down into sugars like a chocolate bar does -- and this is not an energy source that human bodies evolved with.
"We're really designed physiologically to burn fat, it's what our body is designed to do. Shifting the major energy systems from sugar to fat is the transition you go through when you take a gluten-free option," McCraw said.
Read: Will a gluten-free diet help your health?
The first step in treating problems with gluten is to stop eating grain-based foods for at least four weeks, says Everard, but not -- especially for high-performance athletes -- to eliminate carbs altogether.
"We educate the patients about consuming gluten-free ancient whole grains. These include amaranth, buckwheat, corn, millet, uncontaminated organic oats, quinoa, sorghum, teff and rice. This gives the gastrointestinal tract (GIT) a chance to start repairing itself."
It needs help, and probiotics will aid restoration of the stomach's healthy bacteria and digestive enzymes, and also protect against further damage, Everard says.
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"The research and my clinical results have found the GIT is weakened when we are exercising, especially in hot conditions and leaves the body susceptible to illness," he adds.
"The lining of the gut is very sensitive to the intense heat that endurance athletes train under. My patients have often complained of cramping in the gut, diarrhea or nausea and an increase in colds and flus after competitions and intense training.
"As the body heats up, small cracks form in the intestinal wall, allowing bacteria into the blood stream. We monitored our patients and found that when they did extensive exercise 82% showed symptoms of gut discomfort, reduced tolerance to the heat or a decrease in immune function."
In the case of Djokovic, who clinched a record third successive Australian Open title on Sunday, he had to give up childhood staples such as pizza, pasta and pancakes while introducing more vegetables and rice, fruit and sushi for easily digestible protein.
"At first, it was difficult for him but he was fed up of being stuck in third place and his determination to be the champion combined with his confidence in my knowledge was all the motivation that he needed to change his diet," says Cetojevic.
"I also suggested that he cut down on his consumption of meat, particularly before a match. Coming from Serbia, that was a radical suggestion -- even more so than cutting out gluten!
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"Because Novak was in very good condition from his constant training routine, the benefits were apparent almost immediately, which encouraged him to continue. The breathing problem vanished as did the frequent injuries and strains that had been hampering his progress."
McCraw says he has also seen "life-changing" results in his clients.
"Personalities changed, they were much calmer, had more clarity, better grades at school, their relationships with parents have improved, my relationship with them has matured," he said.
"Less sweating on the court, their endurance levels have increased, ability to maintain a leaner figure has improved, ability to build and hold muscle mass has improved. All of the things that an athletic trainer and coach would strive for, I've seen evidence of that on a daily basis."
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However, a gluten-free diet might not suit everyone, says Susie Parker-Simmons, a sports scientist who works with the U.S. Olympic Committee as well as women's tennis players on the WTA Tour.
"There is no benefit in avoiding gluten if you do not have celiac disease or gluten intolerance," she told CNN.
"Therefore I would not recommend an athlete try this diet unless diagnosed by a medical professional."
She said that athletes might find it difficult to adhere to such a diet, especially tennis players who have to travel a lot and might have restricted food options.
"Gluten-free standards and labeling differs in each country. Before going overseas WTA players need to gain advice on the best foods to eat in their country of destination and order gluten-free meals on the airlines they are traveling with," she said.
"A large amount of carbohydrate-rich foods contain gluten in them e.g. bread, pasta, sports bars etc. An athlete with celiac disease needs to be very careful when selecting carbohydrate-based foods to ensure they receive their daily requirements."
Another problem is that many foods containing gluten are also important sources of fiber -- which the body needs to keep the intestines clear of toxins.
"Common gluten-free sources of fiber include: vegetables, fruit, brown rice, legumes, nuts and seeds," Parker-Simmons said.
She believes that while research has shown positive links between health improvement and a gluten-free diet, there is little to suggest it helps in terms of injury prevention and recovery.
McCraw, however, said that his players had shown improved ability to bounce back from intense workouts.
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"There's always micro trauma in the muscles and joints, and the body has a natural anti-inflammatory response to that after exercise," he said.
"The gluten inhibits that process and therefore the onset of muscle soreness is worse. The general ability to recover and retain that homeostatic state is compromised. Your threshold of work levels is lower and your recovery rate is higher and longer."
Everard would like to see more studies into the effects of gluten, which he believes could be at the heart of many modern illnesses.
"This is a very complex area and not fully understood in mainstream medicine, however there is a huge amount of research and evidence in this field," he said.
"I see the benefits of a gluten-free diet in my patients every day through clinical experience, but there still needs to be more research done so that this can become more mainstream -- especially in the world of sport."
Many studies focus solely on the benefits or otherwise of eliminating gluten, rather than taking into account other dietary elements.
"The question is -- is it actually gluten that is the problem or is it refined grains or grains in general?" says British nutritional therapist Kate Delmar-Morgan.
"Individuals wishing to go down this route should seek proper nutrition advice and be tested if possible."
There is also the issue that many gluten-free products are processed and contain high levels of added sugars and artificial additives.
"People will look at these products and think they are 'healthy' just because they are advertised as gluten-free," Delmar-Morgan says.
"However if people stick to a wholefoods diet -- i.e. fresh fish, meats, vegetables, fruit, nuts and seeds, wholegrains which do not contain gluten, and they try to cook from scratch as much as possible and have limited pre-prepared foods -- they can then avoid this problem."
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However, Cetojevic said the problem was Djokovic's intolerance to gluten -- which is found in grains such as wheat and their byproducts -- so he had to eliminate it from his diet and add more fruit, rice, vegetables and fish protein. The Serbian has now won a record three successive Australian Open titles.
This image, provided by Australian naturopathic physician Hamish Everard, shows what blood looks like before going on a gluten-free diet. The cells are clumped closely together.
This image, taken after the subject went on a gluten-free diet, shows the blood cells are able to flow more freely -- allowing better transportation of oxygen around the body.
"After eliminating grains from the patients' diet, all of their symptoms began to resolve within only a few days," says Everard. "Not only did their gastrointestinal symptoms disappear, but so too did other metabolic symptoms such as chronic and general fatigue, diabetes (high and low blood sugar), high cholesterol, decrease in inflammatory markers, soft tissue injuries, joint pain and stiffness, improved cognition (concentration), less anxiety, decreased depression, increase in bone density in osteoporosis patients, eczema, psoriasis and a decrease in acidity levels."
Experts say many health problems stem from changes in food production. "The hybridization of the native European wheat with a shorter, hardier strain from South America in the 1940s produced the particular gluten protein that triggers the sensitivity in people's digestive system," says Cetojevic. "For thousands of years people ate and digested wheat without adverse effects, but we haven't yet adapted to the new protein in the hybrid variety that is now widely grown and marketed for its convenience and higher yield. People are better off eating the older strains such as spelt and kamut."
Pasta is another staple food for many athletes. "Educating people on long-term dietary habits often depends upon how bad they felt before," says Everard. "The worse you were, the more willing you are to make the change. Athletes are disciplined and often do whatever is required of them to improve physically, mentally and emotionally for their sport. I try to teach the 80/20 principle: 80% good 20% bad. Once the underlying causes of gluten intolerance has been corrected, most patients can consume it again in some form or another."
People who are gluten intolerant suffer damage to their intestinal microvilli. "We have seen a definite link in gluten intolerant patients as far as a decrease in beneficial stomach bacteria, an increase in acidity and a decrease in both gastric digestive enzymes and pancreatic enzymes," says Everard.
Cetojevic believes the trend towards gluten-free diets is growing. "In 2011 I saw that most of the players' lounges on the tennis circuit offered gluten-free options, which was not the case in 2010," he says. "I observed that some of the top players have slimmed down and are faster on the court."
Djokovic holds the Norman Brookes Challenge Cup on January 27.
Djokovic hits a return against Murray on January 27.
Djokovic plays a backhand on January 27.
Murray plays a backhand against Djokovic on January 27.
Djokovic serves to Murray at Melbourne Park on January 27.
Murray reacts to a point on January 27.
Murray wipes his face during his men's final match against Djokovic on January 27.
Murray receives medical attention to his foot on January 27.
Crowds cheer during the men's singles final match on January 27.
Djokovic plays a forehand on January 27.
Djokovic plays a smash forehand on January 27.
Murray plays a backhand on January 27.
Murray plays a backhand against Djokovic on January 27.
Four-time Australian Open men's singles champion Andre Agassi carries the Norman Brookes Challenge Cup before the men's final match on January 27.
Murray plays a forehand on January 27.
Victoria Azarenka of Belarus poses with the winner's trophy after defending her Australian Open title on Saturday, January 26. Azarenka defeated Na Li of China 4-6, 6-4, 6-3.
Victoria Azarenka of Belarus celebrates winning her women's final match.
Li Na plays a forehand in her women's final match against Belarus Azarenka.
Belarus Azarenka hits a return during the women's final, which she won 4-6 6-4 6-3.
Li Na falls for the second time during her women's final match.
Benlarus Azarenka reaches for a forehand during Saturday's final.
Li Na rips a forehand Saturday. Li was also a finalist in the 2011 Australian Open.
Belarus Azarenka, who retained her world No. 1 ranking, serves in Saturday's final.
Mike Bryan, left, and his brother, Bob Bryan, of the U.S. celebrate after their victory over the Netherlands' Robin Haase and Igor Sibling during the men's doubles final January 26.
Robin Haase plays a forehand in Saturday's doubles match against the Bryan brothers.
Bob Bryan reaches for an overhead in the men's doubles final.
Nick Kyrgios of Australia serves in his junior boys' final match against Thanasi Kokkinakis of Australia on January 26. Kyrgios captured the boys singles title in straight sets.
Stephane Houdet of France plays a forehand in his men's wheelchair singles final match on January 26 against Shingo Kunieda of Japan. Kunieda won 6-2 6-0.
Sabine Ellerbrock of Germany plays a backhand in her wheelchair singles final against Aniek Van Koot of the Netherlands on January 26. Van Koot took the title with a 6-1 1-6 7-5 victory.
Katerina Siniakova of the Czech Republic plays a forehand in her junior girls' final match against Ana Konjuh of Croatia on Saturday. Konjuh won the championship 6-4 6-4.
Andy Murray of Great Britain plays a backhand in his semifinal match against Roger Federer of Switzerland on January 25. Murray defeated Federer 6-4, 6-7 (5-7), 6-3, 6-7 (2-7), 6-2.
Ashley Barty of Australia, right, watches as compatriot Casey Dellacqua plays a return during their women's doubles final against Sara Errani and Roberta Vinci of Italy on day 12 of the Australian Open in Melbourne on Friday, January 25. The Italian pair beat Barty and Dellacqua 6-2, 3-6, 6-2.
Na Li of China pauses during a news conference on January 25.
Sara Errani and Roberta Vinci of Italy celebrate winning their final doubles match against Ashleigh Barty and Casey Dellacqua of Australia on January 25.
A supporter of Britain's Andy Murray watches during his men's singles semifinal match against Switzerland's Roger Federer on January 25.
Andy Murray of Great Britain plays a backhand on January 25.
Roger Federer of Switzerland plays a backhand on January 25.
Italy's Roberta Vinci, left, and Sara Errani pose with the winner's trophy after their victory over Australia's Ashleigh Barty and Casey Dellacqua on January 25.
Andy Murray of Great Britain takes a breather in his semifinal match against Roger Federer of Switzerland on January 25.
Andy Murray of Great Britain and Roger Federer of Switzerland play their semifinal match in Rod Laver Arena on January 25.
Roger Federer of Switzerland plays a semifinal match against Andy Murray of Great Britain on January 25.
Roger Federer hits a return on January 25.
Andy Murray of Great Britain plays a forehand on January 25.
Novak Djokovic of Serbia celebrates winning his semifinal match against David Ferrer of Spain during the Australian Open in Melbourne on Thursday, January 24. Djokovic won 6-2, 6-2, 6-1.
Djokovic signs autographs for fans on January 24.
Sloane Stephens of the U.S. reacts during her women's singles semifinal match against Victoria Azarenka of Belarus on January 24. Azarenka won 6-1, 6-4.
Na Li of China plays a forehand in her semifinal match against Maria Sharapova of Russia on January 24. Li won 6-2, 6-2.
A tennis fan sits in the stands during Day 11 of the Australian Open at Melbourne Park on January 24.
Li plays a forehand on January 24.
Sharapova plays a return against Li on January 24.
Ferrer plays a backhand on January 24.
Stephens plays a return against Azarenka on January 24.
Djokovic reacts after a point against Ferrer on January 24.
Fans watch the men's semifinal match between Ferrer and Djokovic on January 24.
Azarenka plays a forehand against Stephens on January 24.
Brothers Bob, left, and Mike Bryan battle Simone Bolelli and Fabio Fognini of Italy in a doubles semifinal match on January 24. The brothers won 6-4, 4-6, 6-1.
Stephens plays a return on January 24.
Ferrer plays a backhand against Djokovic on January 24.
Djokovic plays a backhand against Ferrer on January 24.
Stephens pauses during her match against Azarenka on January 24.
Sloane Stephens of the U.S. celebrates after beating compatriot Serena Williams, who was favored to win the tournament, during their women's singles match on Day 10 of the 2013 Australian Open in Melbourne on Wednesday, January 23. Stephens won 3-6, 7-5, 6-4.
Stephens plays a backhand in her quarterfinal match against Williams on January 23.
Williams stares down the ball during her match on January 23 against Stephens.
Williams broke her racket while playing Stephens on January 23.
Williams stretches across the court on January 23.
Italy's Sara Errani plays a backhand in her women's doubles quarterfinal match with compatriot Roberta Vinci against Ekaterina Makarova and Elena Vesnina of Russia on January 23. Errani and Vinci won 6-2, 6-4.
France's Jeremy Chardy hits a return against Britain's Andy Murray during their men's singles match on January 23. Murray defeated Chardy 6-4, 6-1, 6-2.
Murray celebrates beating Chardy on January 23.
France's Jo-Wilfried Tsonga scoops up a return to Switzerland's Roger Federer during their men's singles match on January 23. Federer defeated Tsonga 7-6 (4), 4-6, 7-6 (4), 3-6, 6-3.
Federer plays a backhand to Tsonga on January 23.
Victoria Azarenka of Belarus hits a return against Russia's Svetlana Kuznetsova on January 23. Azarenka defeated Kuznetsova 7-5, 6-1.
Kuznetsova serves during her match against Azarenka on January 23.
Azarenka receives a towel during her match on January 23.
Novak Djokovic of Serbia stretches for the ball in his quarterfinal match against Tomas Berdych of the Czech Republic on Tuesday, January 22. Djokovic won 6-1, 4-6, 6-1, 6-4.
Fans watch Djokovic and Berdych play on January 22.
Berdych plays a backhand in his match against Djokovic on January 22.
Spain's David Ferrer watches the ball during his men's singles match against compatriot Nicolas Almagro on January 22. Ferrer defeated Almagro 4-6, 4-6, 7-5, 7-6 (4), 6-2.
Almagro reaches to smash the ball while playing Ferrer on January 22.
Na Li of China hits a return against Agnieszka Radwanska of Poland in their quarterfinal match on January 22. Li won 7-5, 6-3.
Radwanska stretches for a forehand while playing Li on January 22.
Li serves in her match against Radwanska on January 22.
Russian Maria Sharapova plays a forehand in her quarterfinal match against fellow Russian Ekaterina Makarova on January 22. Sharapova won 6-2, 6-2.
Makarova goes airborne in her match against Sharapova on January 22.
American Serena Williams hits a return against Russia's Maria Kirilenko during their women's singles match on Day Eight on Monday, January 21. Williams won 6-2, 6-0.
Kirilenko plays a backhand against Williams on January 21.
Jo-Wilfried Tsonga of France celebrates winning his fourth-round match against fellow French player Richard Gasquet on January 21. The final score was 6-4, 3-6, 6-3, 6-2.
American Sloane Stephens makes a return against Bojana Jovanovski of Serbia on January 21. Stephens defeated Jovanovski 6-1, 3-6, 7-5.
Bojana Jovanovski serves to Sloane Stephens on January 21.
Roger Federer of Switzerland serves in his fourth-round match against Canadian Milos Raonic on January 21. Federer won 6-4, 7-6(4), 6-2.
Svetlana Kuznetsova of Russia hits a backhand in her fourth-round match against Caroline Wozniacki of Denmark on January 21. Kuznetsova defeated Wozniacki 6-2, 2-6, 7-5.
A ball kid displays Australian Open tennis balls during a match on January 21 at Melbourne Park.
Jeremy Chardy of France serves in his fourth-round match against Italy's Andreas Seppi on January 21. Chardy defeated Seppi 5-7, 6-3, 6-2, 6-2.
Andreas Seppi plays a backhand against Jeremy Chardy on January 21.
Caroline Wozniacki of Denmark returns a backhand in her fourth-round match against Svetlana Kuznetsova of Russia on January 21. Kuznetsova won 6-2, 2-6, 7-5.
Caroline Wozniacki hits a return against Svetlana Kuznetsova on January 21.
Caroline Wozniacki serves in her January 21 match against Svetlana Kuznetsova.
Svetlana Kuznetsova shows off a tattoo on January 21.
Stanislas Wawrinka of Switzerland plays a return during his men's singles match against Serbian Novak Djokovic on Sunday, January 20, Day Seven of the Australian Open in Melbourne, Australia. Wawrinka lost 1-6, 7-5, 6-4, 6-7 (5), 12-10.
Djokovic celebrates his narrow victory January 20 against Wawrinka.
Spain's David Ferrer hits a return against Japan's Kei Nishikori during their men's singles match on January 20. Ferrer won 6-2, 6-1, 6-4.
Nishikori reacts during his match against Ferrer on January 20 as a ballgirl watches.
Ferrer plays a forehand against Nishikori on January 20.
Venus and Serena Williams of the U.S. are congratulated by Russian Nadia Petrova and Slovenian Katarina Srebotnik after winning their third-round doubles match on January 20.
Maria Sharapova of Russia serves in her fourth-round match against Kirsten Flipkens of Belgium on January 20. Sharapova defeated Flipkens 6-1, 6-0.
Sharapova serves in her fourth-round match against Flipkens.
German Julia Goerges, left, congratulates Na Li of China on winning their fourth-round match 7-6 (6), 6-1 on January 20.
Mike Bryan of the U.S. plays a forehand in his third-round doubles match with his twin, Bob Bryan, against Jeremy Chardy of France and Lukasz Kubot of Poland on January 20. The Bryans won 6-7 (4), 6-4, 6-3.
Serbia's Janko Tipsarevic looks at his wrapped foot during a break in his men's singles match against Spain's Nicolas Almagro on January 20. Almagro moved on to the next round after Tipsarevic pulled out of the match in the second set because of his injury.
Kevin Anderson of South Africa prepares to serve in his fourth-round match against Tomas Berdych of the Czech Republic on January 20. Berdych won 6-3, 6-2, 7-6 (13).
Huge crowds gather at Federation Square to watch Bernard Tomic of Australia play Roger Federer of Switzerland on Saturday, January 19. Federer won 6-4, 7-6 (5), 6-1.
Gael Monfils of France twists around to return the ball in his third-round match against compatriot Gilles Simon on Saturday, January 19. Simon defeated Monfils 6-4, 6-4, 4-6, 1-6, 8-6.
Britain's Andy Murray plays a forehand in his third-round match against Ricardas Berankis of Lithuania on January 19.
Maria Kirilenko of Russia celebrates match point in her third round match against Yanina Wickmayer of Belarus on January 19.
Andy Murray serves in his match against Berankis.
Juan Martin Del Potro of Argentina rests in between points in his third-round match against Jeremy Chardy of France.
Philipp Kohlschreiber of Germany serves in his third round match against Milos Raonic of Canada.
Maria Kirilenko of Russia serves in her third-round match against Yanina Wickmayer of Belgium on January 19.
Laura Robson of Britain plays a forehand in her third-round match against Sloane Stephens of the United States on January 19.
Serena Williams of the United States reacts in her third-round match against Ayumi Morita of Japan on January 19.
Maria Kirilenko of Russia plays a forehand in her third-round match against Yanina Wickmayer of Belarus.
Mansour Bahrami of Iran warms up for a doubles match on January 19. He and Wayne Ferreira of South Africa faced Australians Mark Woodforde and Todd Woodbridge.
Juan Martin Del Potro of Argentina serves in his third round match against Jeremy Chardy of France.
A ball kid throws a tennis ball in the third round match between Jeremy Chardy of France and Juan Martin Del Potro of Argentina.
Victoria Azarenka of Belarus plays a forehand in her third-round match against Jamie Hampton of the United States.
Ayumi Morita of Japan serves in her third round match against Serena Williams of the United States, on January 19. Williams won the match 6-1, 6-3.
Serena Williams of the United States plays a backhand in her third round match against Ayumi Morita of Japan, on January 19.
Bojana Jovanovski of Serbia signs autographs for fans after winning her third round match against Kimiko Date-Krumm of Japan, on January 19. The final match score was 6-2, 7-6, tie-breaker 7-3.
The racquets of Bob Bryan of the United States and Mike Bryan of the United States cross as they compete in their men's second round doubles match against Flavio Cipolla of Italy and Andreas Seppi of Italy on Friday, January 18. The Bryan brothers won 6-3, 6-4.
Novak Djokovic of Serbia serves against Radek Stepanek of the Czech Republic during their men's singles match on Day Five of the Australian Open in Melbourne, Australia, on Friday, January 18. Djokovic won 6-4, 6-3, 7-5.
Djokovic plays a forehand in his third-round match against Stepanek on January 18.
Tomas Berdych of the Czech Republic plays a backhand in his third round match against Jurgen Melzer of Austria on January 18. Berdych won 6-3, 6-2, 6-2.
Clouds loom over the stadium in Melbourne Park as Berdych and Melzer compete in their third-round match on January 18.
Stepanek reacts after a shot on January 18.
Ana Ivanovic of Serbia serves in her third-round match against Jelena Jankovic of Serbia on January 18. Ivanovic won 7-5, 6-3.
Maria Sharapova of Russia reacts after beating Venus Williams of the U.S. during their women's singles match on January 18. Sharapova won 6-1, 6-3.
Sorana Cirstea of Romania plays a forehand in her third-round match against Na Li of China on January 18. Li won 6-4, 6-1.
Alex Bolt of Australia plays a backhand in his third-round doubles match with Greg Jones of Australia against Daniele Bracciali of Italy and Lukas Dlouhy of Czech Republic on January 18. Bracciali and Dlouhy won 6-2, 7-6 (4).
Sharapova serves against Williams during their women's singles match on January 18.
Fernando Verdasco of Spain plays a forehand in his third-round match against Kevin Anderson of South Africa on January 18. Anderson won 4-6, 6-3, 4-6, 7-6 (4), 6-2.
Stepanek hits a return against Djokovic during their men's singles match on January 18.
Anderson serves in his third-round match against Verdasco on January 18.
Anderson plays a forehand in his third-round match against Verdasco on January 18.
Williams plays a backhand in her third-round match against Sharapova on January 18.
Berdych plays a return during his men's singles match against Melzer on January 18.
Williams hits a return against Sharapova on January 18.
Marcos Baghdatis of Cyprus hits a return against David Ferrer of Spain during their men's singles match on January 18. Ferrer won, 6-4, 6-2, 6-3.
Baghdatis plays a backhand during his third-round match against Ferrer on January 18.
Jankovic plays a backhand in her third round match against Ivanovic on January 18.
Sorana Cirstea of Romania plays a backhand in her third-round match against Na Li of China on January 18.
Na serves against Cirstea on January 18.
Agnieszka Radwanska of Poland plays a forehand in her third-round match against Heather Watson of Great Britain on January 18. Radwanska won 6-3, 6-1.
Watson serves in her third-round match against Radwanska on Januray 18.
Spectators gather ahead of the start of play on the fifth day of the Australian Open on January 18.
Germany's Angelique Kerber hits a return against Madison Keys of the United States during their women's singles match on January 18. Kerber won 6-2, 7-5.
Keys plays a forehand in her third-round match against Kerber on January 18.
Ball kids dry the court during a rain delay on January 18.
China's Zheng Jie plays a return during her women's singles match against Germany's Julia Goerges on January 18. Goerges won 6-3, 1-6, 7-5.
Goerges plays a return during her women's singles match against Zheng on January 18.
Serena Williams of the U.S. holds her mouth after hitting herself with her racket during her women's singles match against Garbine Muguruza Blanco of Spain during Day Four of the 2013 Australian Open on Thursday, January 17, in Melbourne, Australia. Williams won 6-2, 6-0.
Williams plays a return during her women's singles match against Muguruza Blanco on January 17.
Maria Kirilenko of Russia stretches for a forehand in her second-round match against Shuai Peng of China on January 17. Kirilenko won 7-5, 6-2.
Bernard Tomic of Australia plays a forehand in his second-round match against Daniel Brands of Germany during Day Four of the 2013 Australian Open on January 17. Tomic narrowly defeated Brands 6-7 (4), 7-5, 7-6 (3), 7-6 (8).
Tomic twists around to get a return during his men's singles match against Brands on January 17.
Caroline Wozniacki of Denmark, left, shakes hands with Croatian Donna Vekic on January 17 after defeating her 6-1, 6-4.
Spectators cheer for Croatia's Marin Cilic during his men's singles match against Rajeev Ram of the U.S. on January 17. Cilic won 7-5, 6-2, 6-4.
Andy Murray of Britain plays a backhand in his second-round match against Joao Sousa of Portugal on January 17. Murray defeated Sousa 6-2, 6-2, 6-4.
A young spectator cools off by standing in front of a water vapor machine. Temperatures reached 40 Celsius (104 Fahrenheit).
Victoria Azarenka of Belarus serves in her second-round match against Eleni Daniilidou of Greece on January 17. Azarenka defeated Daniilidou 6-1, 6-0.
Spectators cheer for France's Jo-Wilfried Tsonga during his men's singles match against Japan's Go Soeda on January 17. Tsonga defeated Soeda 6-3, 7-6(1), 6-3.
Novak Djokovic of Serbia plays a backhand in his second round match against Ryan Harrison of USA during on Wednesday, January 16. Djokovic defeated Harrison 6-1, 6-2, 6-3.
Harrison plays a return during his men's singles match against Djokovic on January 16.
Djokovic gestures to the crowd as he celebrates victory over Harrison on January 16.
Serbia's Janko Tipsarevic hits a return against Slovakia's Lukas Lacko during their men's singles match on January 16. Tipsarevic won in five sets, 6-3, 6-4, 3-6, 4-6, 7-5.
A ball girl catches the ball on an outside court late in the day on January 16.
Irina-Camelia Begu of Romania, left, plays a forehand in her second round match against Agnieszka Radwanska of Poland on January 16. Radwanska won 6-3 6-3.
Brian Baker of the United States covers his head after injuring his knee in his second round match against compatriot Sam Querrey on January 16. After winning the first set in a tie breaker, Baker dropped out of the match two games into the second set.
Marcos Baghdatis of Cyprus serves in his second round match against Tatsuma Ito of Japan on January 16. Baghdatis won 3-6 6-3 6-2 6-2.
Tim Smyczek of the United States plays a return during his men's singles match against Spain's David Ferrer on January 16. Ferrer defeated Smyczek 6-0 7-5 4-6 6-3.
Serbian Ana Ivanovic serves in her second round match against Yung-Jan Chan of Taipei on January 16. Ivanovic won 7-5 1-6 6-4.
Roger Federer of Switzerland plays a backhand in his first-round match against Benoit Paire of France during Day 2 of the 2013 Australian Open in Melbourne on Tuesday, January 15. Federer defeated Paire 6-2, 6-4, 6-1.
Germany's Sabine Lisicki plays a return during her women's singles match against Denmark's Caroline Wozniacki on January 15. Wozniacki defeated Lisicki 2-6, 6-3, 6-3.
The courts at Melbourne Park are lit for night play during day two of the tournament on January 15.
France's Gael Monfils reaches for a return during his men's singles match against Ukraine's Alexandr Dolgopolov on January 15. Monfils defeated Dolgopolov 6-7(7), 7-6(4), 6-3, 6-3.
Monfils, right, plays a return to Dolgopolov during their singles match on January 15.
Yanina Wickmayer of Belgium celebrates winning a point in her first-round match against Jarmila Gajdosova of Australia on January 15. Wickmayer defeated Gajdosova 6-1, 7-5.
Gajdosova of Australia struggles to get up after a play during her first-round match against Wickmayer of Belgium on January 15.
France's Richard Gasquet plays a return during his men's singles match against Albert Montanes of Spain on January 15. Gasquet defeated Montanes 7-5, 6-2, 6-1.
Bernard Tomic of Australia plays a backhand in his first-round match against Leonardo Mayer of Argentina on January 15. Tomic defeated Mayer 6-3, 6-2, 6-3.
Thailand's Luksika Kumkhum reacts after a point against Hungary's Timea Babos during their women's singles first-round match on January 15. Kumkhum defeated Babos 7-6(5), 6-4.
Andy Murray of Great Britain serves in his first-round match against Robin Haase of the Netherlands on January 15. Murray defeated Haase 6-3, 6-1, 6-3.
Caroline Wozniacki of Denmark plays a backhand in her first-round match against Sara Errani of Italy on January 15. Wozniacki defeated Lisicki 2-6, 6-3, 6-3.
John-Patrick Smith of Australia plays a forehand on January 15 during his first-round match against Joao Sousa of Portugal. Sousa defeated Smith 6-4, 6-1, 6-4.
A juggler entertains the crowd as they wait to enter the grounds at Melbourne Park for Day 2 of the Australian Open.
A fan gets ready for the Australian Open on January 15.
Serena Williams of the United States falls to the court during her first-round match against Romania's Edina Gallovits-Hall on January 15.
Serena Williams of the United States is helped off the court on January 15 after injuring her ankle. Williams defeated Gallovits-Hall 6-0, 6-0.
Victoria Azarenka of Belarus plays a forehand in her first-round match against Monica Niculescu of Romania on January 15. Azarenka defeated Niculescu 6-1, 6-4.
Great Britain's Andy Murray plays a forehand against Robin Haase of the Netherlands on Day 2 of the Australian Open. Murray defeated Haase 6-3, 6-1, 6-3. Murray won 6-3 6-1 6-3.
Participants work up a sweat during a pre-match cardio workout on January 15.
Dominika Cibulkova of Slovakia plays a backhand in her first-round match against Ashleigh Barty of Australia during the 2013 Australian Open on Monday, January 14. Cibulkova won 3-6 6-0 6-1.
Lleyton Hewitt of Australia plays a backhand in his first-round match against Janko Tipsarevic of Serbia on January 14. Hewitt lost 7-6(4) 7-5 6-3.
The crowd watches the January 14 match between Australia's Lleyton Hewitt and Serbia's Janko Tipsarevic.
Australia's Casey Dellacqua serves against Madison Keys of the United States during their first-round match on January 14. Keys defeated Dellacqua 6-4 7-6(0).
A saturated spectator watches the action on Day 1 of the Australian Open.
Spain's David Ferrer falls to the ground after playing a shot in his first-round match against Belgium's Olivier Rochus on January 14. Ferrer won 6-3 6-4 6-2.
Samantha Stosur of Australia plays a forehand in her first-round match against Kai-Chen Chang of Taiwan on January 14. Stosur won 7-6(3) 6-3.
David Goffin of Belgium plays a forehand in his first-round match against Fernando Verdasco of Spain on January 14. Verdasco defeated Goffin 6-3 3-6 4-6 6-3 6-4.
Serbia's Ana Ivanovic plays a forehand during her first-round match on January 14 against Hungary's Melinda Czink. Ivanovic won 6-2 6-1.
Janko Tipsarevic of Serbia celebrates winning a point in his first-round match against Lleyton Hewitt of Australia on January 14. Tipsarevic won 7-6(4) 7-5 6-3.
Serbia's Novak Djokovic signs autographs for supporters on January 14 after a victory against France's Paul-Henri Mathieu.
Cyprus's Marcos Baghdatis hits a return against Spain's Albert Ramos on January 14. Baghdatis won 6-7(0) 7-6(4) 6-4 3-6 6-3.
Casey Dellacqua of Australia serves in her January 14 match against Madison Keys of the United States. Keys won 6-4 7-6(0).
Venus Williams of the United States serves against Galina Voskoboeva of Kazakhstan on January 14. Williams won 6-1 6-0.
Maria Sharapova of Russia plays a forehand in her first-round match against Olga Puchkova of Russia on January 14. Sharapova won 6-0 6-0 in less than an hour.
Australia's Samantha Stosur plays a return to Taiwan's Kai-Chen Chang during their women's singles match on January 14. Stosur won 7-6(3) 6-3.
Australian tennis fans enjoy the atmosphere during the women's first-round match on January 14 between Sesil Karatantcheva of Poland and Na Li of China. Li won 6-1 6-3.
Germany's Cedrik-Marcel Stebe plays a return to Switzerland's Stanislas Wawrinka during their men's singles match on January 14. Wawrinka defeated Stebe 6-2 6-4 6-3.
Russia's Maria Sharapova plays a backhand in her first-round match against Russia's Olga Puchkova on the first day of the Australian Open.
Japan's Kei Nishikori gestures after playing a stroke to Romania's Victor Hanescu during their men's singles match on January 14. Kei won 6-7(5) 6-3 6-1 6-3.
Pablo Andujar of Spain prepares to serve in his first-round match on January 14 against Xavier Malisse of Belgium. Malisse defeated Andujar 6-3 6-1 6-2.
Switzerland's Stanislas Wawrinka plays a return to Germany's Cedrik-Marcel Stebe on January 14 during their men's singles match. Wawrinka won 6-2 6-4 6-3.
Samantha Stosur of Australia plays a forehand in her first-round match against Kai-Chen Chang of Taiwan on January 14.
Venus Williams
Kim Clijsters
Maria Sharapova alternate
Lindsay Davenport Tennis
Steffi Graf Tennis
Martina Navratilova Tennis
Justine Henin Tennis
Martina Hingis Tennis
Arantxa Sanchez Vicario Tennis
Victoria Azarenka
Caroline Wozniacki
Ana Ivanovic
Li Na
Petra Kvitova
Chris Evert Tennis
Billie Jean King Tennis
His wife Mirka, right, sits with their twins while the 17-time grand slam champion played in a Kids Day exhibition on January 12.
Federer, seeking a fifth Australian Open title, plays with cartoon character Sponge Bob at the children's event.
In December, Federer made a tour of South America, playing exhibition matches in Colombia, Brazil and Argentina.
The 31-year-old said he was touched by the appreciation he received from South American fans. Here supporters in Bogota wear masks with his picture.
Federer controls the ball during a soccer-tennis exhibition match with Argentinian Juan Martin Del Potro and former footballer Gabriel Batistuta (both out of picture) at the Bombonera stadium in Buenos Aires.
Federer wore a Brazilian national football team uniform during an exhibition match against German Tommy Haas in Sao Paulo on December 9.
World No. 3 Murray warmed up for the 2013 Australian Open by winning January's Brisbane International for the second straight year.
Top-ranked Djokovic showed he is in fine form by earlier winning the big-money exhibition tournament in Abu Dhabi and then reaching the final of the Hopman Cup teams event with fellow Serbian Ana Ivanovic.
Djokovic's victory over Roger Federer in the final of the 2012 ATP World Tour Finals gave him the year-end No. 1 ranking for the second season in a row.
Murray beat Roger Federer in the gold medal match at the 2012 London Olympics in August to kickstart a superb run of form.
Djokovic turned the tables on Murray in a superb Shanghai Masters final in October when he saved five match points before clinching an epic victory.
Federer showed his longevity by winning his 17th grand slam at Wimbledon in July 2012, beating Murray in the final
Djokovic bares his chest after completing his epic six-hour, five-set victory over Rafael Nadal to win the 2012 Australian Open title.
Former world No. 1 Nadal hasn't played since being knocked out in the second round of Wimbledon in July 2012, with his expected comeback this year from long-term knee problems being delayed by illness.
Novak Djokovic goes down on his haunches after an spectator barrier collapsed as he was signing autographs.
Djokovic returned to play with Ana Ivanovic in a mixed doubles match for Serbia against Italy.
England rugby player Dean Schofield (second from right) looks far from happy while taking a dip during training in South Africa.
Athletes chill out during the 2007 US Track and Field Championships.
Tennis player Lee Childs suffers for Great Britain ahead of a 2005 Davis Cup clash with Israel.
Ricky Ponting of Australia cools off after making 142 unbeaten runs during a 2002 Test in Pakistan.
Local hero: Andy Murray walks out before an expectant crowd at the O2 Arena in London.
The setting and staging of the ATP World Tour Finals in London has won widespread praise from players and spectators.
A face in the crowd: Hollywood actor Kevin Spacey joined the capacity audiences in London.
The global recession has seen protests across the western world with the Occupy movement taking root outside St Paul's Cathedral in London.
Tennis royalty contested the final of the WTA Championships in Istanbul with Serena Williams beating Maria Sharapova in the final.
Tennis has a global appeal and these fans in Turkey had their own favorite in Russian star Maria Sharapova.
The 2012 tennis season began in earnest in January at the Australian Open. In the final, world No.1 Novak Djokovic and Spain's Rafael Nadal fought a titanic battle before the Serbian emerged on top after five marathon sets.
Murray has reached two grand slam finals and won an Olympic gold medal since hiring Ivan Lendl. Even the great Czech player -- winner of eight majors -- needed four attempts before winning his first final.
Murray, seen here on court in the junior tournament during the 2002 Wimbledon Championships, went to Spain as a teenager to hone his tennis skills.
Murray announced himself as a player to watch with a emphatic victory in the final of the U.S. Open boys' tournament at Flushing Meadows in 2004. The then 17-year-old beat Sergiy Stakhovsky of Ukraine 6-4 6-2.
A 21-year-old Murray lined up against Roger Federer in his first grand slam final at the U.S. Open in 2008. It was a one-sided affair with Federer winning in straight sets 6-2 7-5 6-2 to pick up his 13th major.
Federer once again stood in the way of Murray at the Australian Open in 2010. The match was a bit closer than the 2008 final at Flushing Meadows, but Federer still ran out a comfortable winner 6-3 6-4 7-6.
Murray must have fancied his chances against Djokovic in 2011's Australian Open -- It was his third grand slam final and Federer wasn't his opponent. But his longtime friend provided equally stern opposition, thrashing the Scot 6-4 6-2 6-3.
Murray's fourth attempt to win a grand slam final got off to the perfect start at Wimbledon in July as he took the opening set 6-4 against Federer. But the Swiss champion fought back to win the next three sets, dashing British hopes of a first men's grand slam title since 1936.
Michael Stich celebrates after beating Becker in the first all-German men's final at Wimbledon in 1991, ratcheting up an intensifying battle between the pair which lasted until their retirements in the late 1990s.
Upon beating South Africa in the 1992 Olympic final, Stich and Becker hugged "like brothers" -- a gesture Becker says would have been "impossible" just a week before the tournament.
Strikers Teddy Sheringham (centre) and Andrew Cole (second from right) won a host of trophies at Manchester United together despite barely talking to one another on a social basis.
Tiger Woods and Phil Mickelson were paired together by U.S. Ryder Cup captain Hal Sutton in 2004 in a mistaken belief that the best players in the world would dominate their opponents. The duo lost both matches they played together in a partnership devoid of unity.
Tonya Harding (left) and Nancy Kerrigan studiously avoid one another as they train for the 1994 Winter Olympics, just one month after Harding's former husband had hired an assailant to break Kerrigan's legs. The latter had the last laugh as she took Olympic silver, with Harding finishing eighth.
Cricketer Kevin Pietersen (right) was dropped from the England team after sending "provocative" texts about his own teammates to rival South African players while the two sides were playing Test matches against one another earlier this year.
Ayrton Senna (left) and Alain Prost (centre) in happier times during the early stages of their tempestuous spell together at McLaren, which prompted the Frenchman to abandon the team midway through the Brazilian's second year.
Senna is given a push for a restart while Prost abandons the race after the supposed teammates collided during the Japanese Grand Prix in 1989.
A grieving Prost (second from left), whose relationship with Senna changed after retirement and who says that a part of him died when the 34-year-old suffered a fatal crash in 1994, carries the Brazilian's coffin at his funeral in Sao Paulo.
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