Borja - Two-time Tour of Spain winner Alberto Contador took the overall lead in this year's edition on Tuesday as German Tony Martin won the 10th stage, a 36.7-kilometre time-trial.
Contador, 31 and who finished fourth, 39 seconds slower than triple time-trial world champion Martin, replaced Colombian rider Nairo Quintana in the overall leader's red jersey.
For Contador it represents quite a comeback after, like Chris Froome, he failed to finish the Tour de France because of injury, in his case a broken tibia.
"Nobody ould have imagined that I would be in red today, it is an enormous surprise," the Tinkoff team leader told Spanish TV station TVE.
"As a result of that I really believe I can win."
Quintana, who took a three-second lead on Sunday, came to grief when he fell after a dozen kilometres, as he was bending down to fiddle with his right shoe, and lost more than three minutes to Contador.
Quintana, bidding for a second Grand Tour win this season having won the Tour of Italy, limited the damage somewhat in the remainder of the stage and lies in 11th spot.
"It seems at first sight that I have only grazes," said Quintana on crossing the line.
"We will see tomorrow how I feel. My objective in this Tour after all is to help Alejandro Valverde and we will see in the mountains if I can do something for him."
Contador, winner of the Vuelta in 2008 and 2012, extended his lead over all his major rivals for overall victory as he was 21sec faster than compatriot Valverde and 53sec quicker than Britain's 2013 Tour de France winner Froome, who failed to fire even though on paper he was the best of the time-trialists amongst the race favourites.
Wednesday's 11th stage is a 153.4km ride from Pamplona to San Miguel de Aralar in the northern community of Navarre and will be one for the climbers as it finishes at altitude.
Results from the Tour of Spain after Tuesday's 10th stage, a 36.7 kilometres ride from Monasterio de Veruela to Borja:
1. Tony Martin (GER/Omega Pharma) 47min 02sec, 2 Rigoberto Uran (COL) at 15sec, 3. Fabian Cancellara (SUI) 18, 4. Alberto Contador (ESP) 39, 5. Samuel Sanchez (ESP) 48, 6. Cadel Evans (AUS) 49, 7. Vasil Kiryienka (BLR) 58, 8. Alejandro Valverde (ESP) 1min, 9 Jesse Sergent (NZL) 1:13, 10. Chris Froome (GBR) 1:32. 11. Pieter Serry (BEL) 1:32, 12. Jerome Coppel (FRA) 1:35, 13. Bob Jungels (LUX) 1:39, 14. Romain Sicard (FRA) 1:45, 15. Winner Anacona Gomez (COL) 1:45.
1 Alberto Contador (ESP/Tinkoff) 36hr 45min 49sec, 2. Alejandro Valverde (ESP) at 27sec, 3. Rigoberto Uran (COL) 59, 4. Winner Anacona Gomez (COL) 1min 12sec, 5. Chris Froome (GBR) 1:18, 6. Joaquin Rodriguez (ESP) 1:37, 7. Samuel Sanchez (ESP) 1:41, 8. Fabio Aru (ITA) 2:27, 9. Robert Gesink (NED) 2:38, 10. Damiano Caruso (ITA) 2:59. 11. Nairo Quintana (COL) 3:25, 12. Wilco Kelderman (NED) 3:29, 13. Daniel Martin (IRL) 3:48, 14. Mikel Nieve Ituralde (ESP) 3:50, 15. Warren Barguil (FRA) 4:11.