Armstrong is five stages from glory

The American leads German rival Jan Ullrich by 67 seconds with one more day in the mountains and a crucial individual time trial to come.

Armstrong went into Monday's stage 15 with a slender 15-second advantage over 1997 winner Ullrich and the defence of his crown hanging by a thread.

But in true champion's fashion he dug deep to extend the gap with victory at the mountain top finish of Luz-Ardiden.

Kazakhstan's Alexandre Vinokourov is in third place, two minutes 45 seconds adrift.

I can't see Ullrich taking 67 seconds out of Lance, not in a flat time trial CSC deputy Sean Yates

Wednesday's 197.5km stage 16 from Pau to Bayonne, across two first category climbs, offers Armstrong the chance to consolidate his lead - or his attackers a last-gap opportunity to claw back some vital seconds.

But the last big climb, the Col de Bagargui, is 87km from the finish, and the long, flat run-out should offer chasing teams plenty of time to reel in a breakaway.

"I doubt there will be any change in the overall standings, unless Ullrich does some sort of epic," said Britain's former Tour rider and Team CSC number two Sean Yates, speaking to this website.

"It's a long way from the top of the climb to the finish and Lance will rally the troops and chase him down."

After that the race returns to the flat, and the sprinters will once again come to the fore, before Saturday's crucial time trial, a 49km sprint from Pornic to Nantes.

Ullrich took 1:35 out of Armstrong in the 47km time trial on stage 12 and another resounding victory for the German would leave Armstrong no chance to hit back before Sunday's finish in Paris.

"It could go either way for the result. But I can't see Ullrich taking 67 seconds out of Lance, not in a flat time trial. It could be 20-30 seconds," said Yates.