The three-time Vuelta winner rode a solid time trial on Stage 19 to move ahead of Orica-BikeExchange's Esteban Chaves on the general classification.
Contador posted a time of 48min 30sec over the 37km TT course between Xàbia and Calp to place him over a minute ahead of Chaves and into third place overall.
"I got off to a good start and the first part of the time trial went very well," Contador said. "There was a strong wind but I knew it was there I could make a difference on Chaves. Then it became tougher and I had a hard time keeping a steady pace of watts, it
"Then it became tougher and I had a hard time keeping a steady pace of watts, it was stop and go. I didn't feel the way I would have liked, the effort took its toll but I'm satisfied with the result."
There is one last chance for Contador to make an even bigger mark at the Vuelta, but it would take a supreme effort and forces beyond his control for another favourable change in the general classification to eventuate.
"Froome did an extraordinary race today. Maybe they still have options, but they will, obviously, have to make a move tomorrow. It will be all or nothing for them and we'll see whether we can take advantage of that. I will try something on the Alto de Aitana."
Despite losing ground fourth place Chaves remains optimistic of regaining the position he lost to Contador and see the penultimate stage as one which suits his abilities.
Stage 20 runs 193.2km and covers five classified climbs including the 21km above category 21km Alto de Aitana at the finish.
"Tomorrow is a tough stage, but it’s good for riders like me who weigh less than 60kg," Chaves said. "The race is not over until it’s finished and we will try to do our best with the team. There’s a lot of vertical gain left and we will give everything to be on the podium ”