Lance Armstrong insists victory is not yet his in this year's Tour de France despite taking a firm grip of the race.
The five-time champion won stage 15 on Tuesday to give himself a one minute 25 second lead over Ivan Basso.
But ahead of arguably the Tour's toughest stage - the Alpe d'Huez time trial on Wednesday - Armstrong said: "I don't think it's over by any means.
"Ivan is riding superbly at the moment. I think he can ride a good race in the time trial."
Wednesday's stage is just a 15.5km race against the clock, with the riders going in reverse order, which means Armstrong will be setting off last.
Iban Mayo had been the overwhelming favourite to win the time trial, having obliterated the field on a similar route in the Dauphine Libere in June.
But the Basque rider pulled out of the race with a suspected virus on Tuesday - and Armstrong is determined to notch up a third stage win in this year's race.
"Alpe d'Huez is one of the stages I've worked really hard for," said the American. "I have a friendship with the mountain."
Armstrong has won on Alpe d'Huez before, topping the field there in 2001.
And he admitted he is determined to hold onto the leader's yellow jersey - which he regained on Tuesday - until the end of the race.
"I still remember when I put on the first one and I was the happiest man in the world, that would have been enough for me to take to the grave," he said.
"Hopefully I'll have it for another five days."
But Basso aims to give Armstrong a hard time in the final stages.
"I decided not to attack because the time trial to L'Alpe d'Huez will be a very important head-to-head battle and then there's another mountain stage the day after," said the Italian.
"I'll try to attack then if I've got the strength."