Alberto Contador of Team Saxo Bank has assumed the overall lead of the Vuelta a Espana in dramatic fashion after Joaquin Rodriguez endured a dreadful 17th stage.

Rodriguez (Katusha) went into the final five legs of the 21-stage race with a healthy 28-second lead after outpacing his fellow Spaniard in Monday's gruelling mountain climb.

But his prospects of winning a first-ever major race are now in jeopardy as he struggled to attack the Collado La Hoz, a second category climb towards the finish line at Fuente De.

Pushed into third place by Alejandro Valverde of Movistar, who with Contador outsprinted chase leader Sergio Henoa (Team Sky) to the line, Rodriguez now sits two minutes and 28 seconds off the lead with four stages remaining.

Contador established his daunting one minute and 52 second lead over Valverde before getting out of his saddle to pass Henoa and solo over the line to claim the red jersey.

Ireland's Nicolas Roche endured a disappointing day, finishing 26th on the stage and dropping to 12th overall.

Following a rest day, today's 187km route began in Santander with Gabriel Rasch of FDJ-BigMat mounting an early attack.

Rodriguez was soon caught out as the peloton split at the halfway stage, just about managing to regain his place in the leading pack with Contador steadily extending his lead on the Collado La Hoz.

But Rodriguez floundered without the help of his team-mates and was totally left behind as Contador turned the Vuelta standings upside down with a searing sprint to the finish line.

Team Sky's Chris Froome remains five minutes off the pace but held on to fourth place in the overall classification today.