Alberto Contador admitted to being pushed to his absolute limits on his way to virtually securing a third yellow jersey triumph on the Tour de France on Sunday.

"This year there were times when I wasn't exactly on top form, today included. The race this year was particularly hard," said Contador, who came close to losing his yellow jersey to Andy Schleck in Saturday's final time trial.

Spain's two-time champion went into the penultimate stage time trial with only an eight-second lead on key rival Andy Schleck.

And there was drama right to the wire as Schleck threatened to close his deficit early on before he ran out of juice and Contador came into his own in the latter half of the flat 52km-long course.

In 2009 Contador beat Swiss Olympic champion Fabian Cancellara by three seconds in the final time trial to claim the stage, and rubber-stamp his second yellow jersey triumph.

And despite finishing only 35th, at 5min 43sec behind a victorious Cancellara here on Saturday, it was enough to keep Schleck at 31secs adrift and heading for a second successive runner-up place.

Contador went into Sunday's final stage to Paris, which is not usually contended by the yellow jersey rivals, with a 39sec lead on the Luxemburger. Ironically, it is the exact figure Schleck lost to Contador on stage 15 when the Spaniard counter-attacked him moments before he suffered an untimely mechanical problem with his gears.

Contador admitted he feared for his yellow jersey throughout the 19th stage race against the clock.

"To be honest, I got some information that said I was five seconds behind Andy, and I started to panic," said the Spaniard.

"I started to think, 'Oh my God, this is it, it's over'. And I stayed that way until the finish line really."

With Schleck pushing him so close, Contador knows he is in for a battle in the future. But the Spaniard attempted to put that in perspective by claiming he was not as good as he should have been.

"I know Andy well, and he's a great rider. He's going to be a major rival for a long time," said Contador. "But I think this year I wasn't exactly at my best.

"Things eventually went well for me today but last night, for example, I didn't sleep well and I also had a stomach ache."

Contador also began the race with a cold, which forced him out of the Spanish time trial championships, and from then on it was about managing the dozens of little details that go into fighting for the race's yellow jersey.

"A few days before the Tour I was on antibiotics, and I think this affected my form for the first week," he said.

"From a mental point of view, it was very complicated. I had to stay focused all the time, especially on the climbing stages."