Chris Froome extended his overall lead in La Vuelta after Colombian rider Miguel Angel Lopez won the mountainous 129-kilometre 15th stage from Alcala la Real to Sierra Nevada.

Team Sky rider Froome, who is bidding to become only the third rider to win La Vuelta and the Tour de France in the same year, produced a late surge to stretch his advantage over Vincenzo Nibali by six more seconds.

A top ten finish now looks to be beyond Irish rider Nicolas Roche as he endured a tough day which saw him finish 16:18 behind Lopez and he dropped to 17th in the overall standings, now trailing Froome 21:40.

Froome now has a 61-second cushion over his Italian rival. Lopez finished the stage in three hours, 34 minutes and 51 seconds, overtaking Briton Adam Yates on the final climb to reach the 2,510-metre summit of Alto Hoya de la Mora first for his second win of the race.

Russia's Ilnur Zakarin came second, 36 seconds behind, with Dutchman Wilco Kelderman third and Froome coming in fifth. Zakarin and Kelderman are third and fourth in the general classification but trail Froome by more than two minutes.