Veteran cyclist Chris Horner, 41, wins Tour of Spain

(CNN) -- Belying his 41 years and 327 days, Chris Horner has defied sporting convention by wrapping up victory in the Tour of Spain Sunday.

The American, who rides for the RadioShack-Leopard team, maintained his 37-second advantage over Italian Vincenzo Nibali, the reigning Giro d'Italia champion, after the final stage in Madrid.

Home hope Alejandro Valverde, a former winner of La Vuelta, finished third.

Australian Michael Matthews won the final stage after a bunch sprint, but all the focus was on Horner in the red jersey of overall leader as he finished safely in the main bunch.

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At an age when most professional sportsmen are long retired, Horner has claimed one of cycling's three Grand Tours, the other races being the famed Tour de France and the Giro.

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Initially taking the lead on the third of 21 stages, Horner battled 2010 Vuelta winner Nibali throughout the three-week long endurance test.

Nibali went into the final week with a 50-second advantage, but Horner nibbled at the lead until taking it for the final time on Friday's 19th stage.

Extending it to over half a minute after the brutal 12km climb to Alto de L'Angliru on the penultimate day, Horner merely had to stay upright on the flat final leg to seal his improbable triumph.

"I have faced younger and great riders like Nibali, Valverde and Joaquim Rodriguez," he told gathered reporters.

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"They have had a great tour so for me it is a legendary moment that may not be repeated.

"I know I am also the first North American to win the Tour of Spain and this makes me very proud of my work and above all that of my teammates."

Horner is the oldest winner of one of cycling's three majors by some margin. Switzerland's Tony Rominger was eight years younger when winning the Tour of Spain in 1994 and the oldest Tour de France winner is Fermin Lambot, who was 36 when he triumphed in 1922.

The oldest rider in today's professional peloton is Germany's Jens Voigt, who turns 42 on Tuesday, but now rides as a support rider for Horner's RadioShack team.

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Horner, whose best finish in the Tour de France is 10th place, also played a similar role for the now disgraced Lance Armstrong with the Astana and RadioShack squads, but has achieved his best results since his infamous compatriot retired.

His La Vuelta heroics have now earned him a place in the sporting record books that will be difficult to match.