Alexandre Vinokourov rode to his second Tour de France stage win in three days on the second day in the Pyrenees.
Vinokourov was intent on attacking throughout the day
Vinokourov was part of a 25-man breakaway for much of the day before making a decisive move on the Col de Peyresourde, 21.5km from the finish.
He came home 51 seconds ahead of Kim Kirchen and Haimar Zubeldia.
Denmark's Michael Rasmussen retained the overall leader's yellow jersey, two minutes 23 seconds ahead of Alberto Contador, after a testing 15th stage.
But the two leaders took more time out of all their major rivals after an epic battle on the slopes of the Col de Peyresourde.
When Contador attacked, the only man who could stick with him was Rasmussen.
The Spaniard tested the race leader with repeated short, sharp bursts but was unable to shake him on the run in to Loudenvielle-Le Louron.
They crossed the line 56 seconds ahead of anyone else who started the day in the top 10 and Cadel Evans is now four minutes off top spot in third place.
"The only person I have to worry about now is Contador," said Rasmussen.
Early in the day Rasmussen was happy to let a group that included top-20 riders Zulbedia, Kirchen, David Arroyo as well as Vinokourov go up the road.
And once they were allowed to build up an advantage of more than nine minutes prior to the out-of-category climb of the Port de Bales, it was clear the winner would come from the breakaway.
Pre-race favourite Vinokourov, who lost almost 30 minutes on the first day in the Pyrenees, sat tight, while rivals jockeyed for position, before making his move on the first-category Col de Peyresourde.
"I know it well and I said this morning that I wanted to give it a try," he said of the climb.
"Yesterday, I had no strength. I told myself the Tour is over but I got the support of the whole team."
Despite this success, his fifth in the Tour de France, he will remain a distant bystander as Rasmussen and Contador fight out the top honours.
And after a rest day the pair will renew their rivalry in the final mountainous stage of the Tour, a 218km route through the Pyrenees that features four big climbs.
Contador knows he has to attack to have any hope of overhauling the Dane.
Stage 15 result:
Foix to Loudenvielle-Le Louron (196km)
1. Alexandre Vinokourov (Kaz) Astana 5 hrs 34 mins 28 secs
2. Kim Kirchen (Lux)e T-Mobile @ 51 secs
3. Haimar Zubeldia (Spa) Euskaltel @ same time
4. Juan Jose Cobo (Spa) Saunier Duval @ 58 secs
5. Juan Manuel Garate (Spa) Quick-Step @ 2 mins 14 secs
6. David Arroyo (Spa) Caisse d'Epargne @ 3 mins 23 secs
7. Bernhard Kohl (Aut) Gerolsteiner @ 4 mins 25 secs
8. Christian Vande Velde (USA) Team CSC @ same time
9. Ludovic Turpin (Fra) AG2R @ 5 mins 16 secs
10. Alberto Contador (Spa) Discovery @ 5 mins 31 secs
11. Michael Rasmussen (Den) Rabobank @ 5 mins 31 secs
13. Cadel Evans (Aus) Predictor-Lotto @ 6 mins 27 secs
16. Levi Leipheimer (USA) Discovery @ same time
17. Andreas Kloden (Ger) Astana @ same time
19. Carlos Sastre (Spa) Team CSC @ same time
57. Charlie Wegelius (GB) Liquigas @ 21 mins 9 secs
80. David Millar (GB) Saunier Duval @ 28 mins 25 secs
149. Bradley Wiggins (GB) Cofidis @ 35 mins 45 secs
151. Geraint Thomas (GB) Barloworld @ 35 mins 45 secs
1. Michael Rasmussen (Den) Rabobank 69 hrs 52 mins 14 secs
2. Alberto Contador (Spa) Discovery @ 2 mins 23 secs
3. Cadel Evans (Aus) Predictor-Lotto @ 4 mins
4. Levi Leipheimer (USA) Discovery @ 5 mins 25 secs
5. Andreas Kloden (Ger) Astana @ 5 mins 34 secs
6. Carlos Sastre (Spa) Team CSC @ 6 mins 46 secs
7. Haimar Zubeldia (Spa) Euskaltel @ 7 mins 27 secs
8. Andrey Kashechkin (Kaz) Astana @ 7 mins 54 secs
9. Kim Kirchen (Lux) T-Mobile @ 8 mins 24 secs
10. Mikel Astarloza (Spa) Euskaltel @ 9 mins 21 secs
23. Alexandre Vinokourov (Kaz) Astana @ 28 mins 21 secs
61. Charlie Wegelius (GB) Liquigas @ 1 hr 36 mins 5 secs
76. David Millar (GB) Saunier Duval @ 1 hr 52 mins 15 secs
138. Bradley Wiggins (GB) Cofidis @ 2 hrs 42 mins 20 secs
158. Geraint Thomas (GB) Barloworld @ 2 hrs 59 mins 58 secs