JACA-FUERTE DE RAPITAN, Spain - Spain's Joaquim Rodriguez strengthened his hold on overall race lead in the Vuelta a Espana with a last-minute surge for the line at Fuerte de Rapitan's uphill finish to win Thursday's sixth stage.

Katusha Team rider Joaquim "Purito" Rodriguez of Spain crosses the finish line to win the sixth stage of the Tour of Spain "La Vuelta" cycling race between Tarazona and Jaca August 23, 2012. [Photo/Agencies]

Timing his effort perfectly, Rodriguez finished five seconds clear of Britain's Chris Froome, second in the overall standings, on the four-kilometre climb to an old fort. Alejandro Valverde of Spain was third, 10 seconds back.

Pre-race favourite Alberto Contador, who returned from a doping ban earlier this month, had an off-day and dropped back in the final kilometre as Froome accelerated hard, to finish 18 seconds off the pace.

Following the Vuelta's third summit finish in four days, Katusha rider Rodriguez has increased his lead over Tour de France runner up Froome from one second to 10. Contador remains in third but slid to 36 seconds adrift.

"I barely had the strength to follow Froome, so I had to race intelligently," said Rodriguez, who was congratulated by the Team Sky rider on his performance.

"A team mate (Spain's Angel Vicioso) had checked out this climb beforehand and told me exactly what it was like and I have to thank him, that information was spot on and really valuable," Rodriguez told reporters.

"I stuck on Chris's wheel for most of the climb, I kept going at his pace, and then I just had the strength to nip round him at the finish."

After the final rider of a day-long breakaway, Belgian Thomas De Gendt, was captured by the bunch in the streets of the finishing town of Jaca, Froome's Team Sky made the running on most of the short but painfully steep final climb.

First Columbian Sergio Henao and then Rigoberto Uran brutally upped the pace, with Froome's last drive shaking off both Contador and Valverde but not Rodriguez.

Fourth in the 2010 Vuelta and second in this year's Giro d' Italia, the Spaniard said he was not surprised at Froome's impressive performance.

"Froome was arguably the strongest rider in the Tour and it's clear he's come here with the idea of winning," Rodriguez said.

"For a rider who supposedly wasn't going to be at his best on a climb as steep as this, he's done it very well."

As for his own chances, the 33-year-old said: "I'm doing very well, I feel strong and I've got a very similar team to the one I had in the Giro, which is very important, we know how to work well together." The Vuelta finishes on Sunday Sept. 9 in Madrid.