Spaniard Alberto Contador launched a major attack on the climb up to Verbier to win Stage 15 and put himself in pole position to win the Tour de France.
The 2007 champion left Astana team-mate Lance Armstrong in his wake with 5.6km left to take over the yellow jersey.
He opened up a lead of one minute, 37 seconds over Armstrong in the overall standings, with Bradley Wiggins moving up to third, nine seconds further back.
A superb display of climbing saw the Briton take fifth in the Alpine stage.
Armstrong, who some predicted would mount a strong challenge on the final climb, could only finish ninth, one minute 35 seconds adrift, to leave his hopes of an eighth Tour victory looking remote.
"When Alberto went he showed he is the best rider, showed he is the best climber. You know when everybody is on their limits and you can accelerate again, that's how you win the Tour," said the American, who all but conceded victory to Contador.
"I saw I was opening a gap and just kept on going. I'm extremely happy about the gap to my rivals"
"The race, for me that's not possible," he added. "When somebody has so much pressure on him and shows he is the best you can't deny it. Hats off to him."
Armstrong, who admitted he "suffered" on the final climb, also vowed he would not attempt to go against team orders and attack his team-mate.
"That's not going to happen," he added. "There's been a lot of drama about Alberto and me but at the end of the day we all sit around the table as a team, and the last thing we can do is to lose the Tour."
After days of little movement in the race for overall victory, Contador's explosive charge 5.6km from the finish injected much-needed momentum into this year's Tour.
606: DEBATE" Awesome performance by Contador, great stuff from Wiggins. "
"When I came out of the peloton, I attacked before I intended to, but looking at the situation I decided to have a go at it," said the Spaniard.
"I saw I was opening a gap and just kept on going. I'm extremely happy about the gap to my rivals."
Saxo Bank's Andy Schleck finished closest to the Spaniard, 43 seconds behind, to move up to fifth overall, with Vincenzo Nibali third and Frank Schleck fourth on the day.
The previous yellow jersey holder, Italian Rinaldo Nocentini, dropped down to sixth overall.
It was also a stunning performance by Wiggins, who finished the stage alongside the defending champion Carlos Sastre, the pair having pulled away from a small group containing Cadel Evans, Armstrong and Kloden in the final two kilometres.
"It's a long way to go, let's not get too excited"
Wiggins, a three-time Olympic gold medallist in individual and team pursuit events, is contemplating quitting the track to concentrate on more major road races.
"It's really fantastic, I don't know what to say," said a pained Wiggins, who has shed seven kilograms since his last Tour de France in 2007, and now weighs 72kg (11 st 4lb).
"I'm in great shape, I just keep thinking that. I kept that in my mind."
If he holds onto third place or better in the final week, he would beat the previous best finish by a Briton in the Tour, Robert Millar's fourth in 1984.
But the Londoner refused to look too far ahead, with two more challenging Alpine stages after Monday's rest day before Thursday's individual time-trial, and the fearsome climb to Mont Ventoux on Saturday before the finish in Paris next Sunday, 26 July.
"I keep going day by day, I never think too far ahead," Wiggins added. "I've trained for this mentally and physically.
"How can you think three days ahead when you've got two days before? That's how you crack. It's a long way to go, let's not get too excited."
Stage 15 result:
1. Alberto Contador (Spa/Astana) 5 hours 03 minutes 58 seconds
2. Andy Schleck (Lux/Saxo Bank) + 0:43
3. Vincenzo Nibali (Ita/Liquigas) + 1:03
4. Frank Schleck (Lux/Saxo Bank) + 1:06
5. Bradley Wiggins (GB/Garmin) + 1:06
6. Carlos Sastre (Spa/Cervelo) + 1:06
7. Cadel Evans (Aus/Silence Lotto) + 1:26
8. Andreas Kloden (Ger/Astana) + 1:29
9. Lance Armstrong (US/Astana) + 1:35
10. Kim Kirchen (Lux/Columbia) +1:55
Selected others:
19. Rinaldo Nocentini (Ita/AG2R) +2:36
47. Charlie Wegelius (GB/Silence-Lotto) +4:58
103. David Millar (GB/Garmin) +12:11
130. Mark Cavendish (GB/Columbia) +18:12
Overall standings:
1. Alberto Contador (Spa/Astana) 63 hours 17 minutes 56 seconds
2. Lance Armstrong (US/Astana) +1:37
3. Bradley Wiggins (GB/Garmin) + 1:46
4. Andreas Kloden (Ger/Astana) +2:17
5. Andy Schleck (Lux/Saxo Bank) +2:26
6. Rinaldo Nocentini (Ita/AG2R) +2:30
7. Vincenzo Nibali (Ita/Liquigas) +2:51
8. Tony Martin (Ger/Columbia) +3:07
9. Christophe Le Mevel (Fra/FDJ) + 3:09
10. Franck Schleck (Lux/Saxo Bank) +3:25
Selected others:
11. Carlos Sastre (Spa/Cervelo) + 3:52
14. Cadel Evans (Aus/Silence Lotto) + 4:27
59. David Millar (GB/Garmin) + 40:34
64. Charlie Wegelius (GB/Silence-Lotto) + 41:46
139. Mark Cavendish (GB/Team Columbia) + 1:49:01
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