Ivan Basso won the 12th stage of the Tour de France to La Mongie, but the day belonged to Lance Armstrong.
Armstrong and his US Postal team set the pace up the final climb in the Pyrenees which proved too hot for most.
Basso crossed the line first in 5:03:57, but Armstrong was happy to claim second, gain time on his rivals and move second in the overall standings.
Jan Ullrich finished 2:30 back with Tyler Hamilton at 3:27, but Thomas Voeckler held on to the yellow jersey.
Much of the day passed without incident, merely acting as the calm before the storm of the final first category climbs over the Col d'Aspin and then on to La Mongie.
Armstrong's US Postal team hit the front as the road began to rise, but were happy to let individual raiders off the front.
Rabobank's Michael Rasmussen took the honours over the Col D'Aspin from Christophe Moreau and Richard Virenque.
But by the foothills of the assault on La Mongie, the lead group were back as one, bar Rasmussen, and with Armstrong's team-mate Jose Azevedo setting the pace in the chase group it was only a matter of time before the Dane was overhauled.
That duly came, but what was not expected was the trouble Armstrong's main rivals had in staying with the group.
Hamilton, who has been suffering with a back injury since a crash on stage six, quickly drifted off the back, as did Ullrich.
Finally it became a straight race between Basso and Armstrong over the closing stages and as the pair approached the finishing line the Italian edged ahead to take the honours.
But Armstrong took the plaudits, most notably from Basso.
"The first contact with high mountains has been harder for the other Tour favourites and from what we've seen, Lance is obviously the strongest," the CSC team leader said.
"It was the first mountain stage and the weather conditions may have worked Lance's way as he likes the rain."
As well as opening up a gap on the likes of Ullrich and Hamilton, Armstrong closed the margin to Voeckler in yellow.
The young Frenchman came home 3:59 down, a brave ride that ensured he held on to the lead, although Armstrong moved from sixth to second overall, cutting the deficit to 5:24.
Sandy Casar of FDJeux.com lies third at 5:50, but Ullrich is now 9:01 adrift in 16th place overall with Hamilton in 20th at 9:46.
Saturday's 13th stage features another day of intense climbing on a 205.5-km ride from Lannemezan to Plateau de Beille.