Sastre made his move at the bottom of L'Alpe-d'Huez
Spain's Carlos Sastre took the yellow jersey after winning the final alpine stage of the Tour de France but Cadel Evans is favourite for overall victory.
Sastre made his surprise move on the famous L'Alpe-d'Huez and powered on to grab the overall lead from his CSC team-mate Frank Schleck of Luxembourg.
He leads Schleck by one minute and 24 seconds, with Evans 10 seconds back.
But Evans is expected to make up the lost time during Saturday's time trial in the penultimate stage of the Tour.
Austria's Bernhard Kohl is one second ahead of Evans in third place but Denis Menchov, who lies a minute and five seconds behind the Australian in fifth, is another exceptional time-trialist and remains dangerous.
I suffered a lot on the way to the summit but I take great pleasure in capturing the jersey
Apart from Sastre, who sped clear at the foot of the final climb, all the major contenders finished together.
The 33-year-old Spaniard, a five-time top-10 finisher in the Tour, crossed the line over two minutes ahead of his nearest rival to end an intriguing final day in the Alps.
With Sastre and Schleck both well placed at the start of the stage, CSC's tactic's were under scrutiny as they looked to break Evans over the three major climbs of the day - the Galibier, Croix de Fer and l'Alpe d'Huez.
At times there were six CSC riders at the head of the peloton and the pace they set on the Croix de Fer was too hot for most of the other riders.
Evans and Kohl stuck with them, however, until Sastre's electric burst took him clear on Huez.
"I suffered a lot on the way to the summit but I take great pleasure in capturing the jersey," Sastre said. "It's a dream come true.
"A pure climber has to take advantage of his opportunities, and this was mine. I had to take the risk of attacking from the beginning of the Alpe d'Huez."
Euskatel rider Samuel Sanchez finished second to make it a Spanish one-two, with Frank Schleck's brother Andy third for CSC.
Despite appearing exhausted and receiving no help from the riders around him, Evans battled to the line to limit his losses.
His efforts were almost certainly enough to end Frank Schleck's hopes of overall victory as he only gained two seconds on Evans, who is a vastly superior time-trialist.
The riders now face two mainly flat stages before Saturday's 53km time trial from Cerilly to Saint-Amand-Montrond - where Evans will be expected to prevail.
"I have two days to enjoy the yellow jersey and on Saturday I will think about the time trial," Sastre added.
"I will find out then if I am able to win the Tour."
Evans admitted he felt vulnerable on Huez and feels his victory is far from certain.
"When you have the 10 best bike riders in the world behind your wheel and you have a two-minute gap to close on one of the best climbers in the world, it's not any situation to be in," Evans said.
"It will take a good time trial to win the Tour. I hope that I will have the legs on Saturday - we will see."
Meanwhile, Saunier Duval has pulled out of cycling because of the involvement of the team it sponsored in doping incidents at this year's Tour.
Italian rider Riccardo Ricco, who won two stages this year, and his team-mate Leonardo Piepoli were thrown off the Tour last week after testing positive for EPO.
Stage 17 results, Embrun to L'Alpe-d'Huez (210.5km):
1. Carlos Sastre (Spain/Team CSC) 6hrs 7min 58sec 2. Samuel Sanchez (Spain/Euskalte) +2min 3 sec 3. Andy Schleck (Luxembourg/Team CSC) same time 4. Alejandro Valverde (Spain/Caisse d'Epargne) +2min 13sec 5. Frank Schleck (Luxembourg/Team CSC) same time 6. Vladimir Efimkin (Russia/AG2R) +2min 15sec 7. Cadel Evans (Australia/Silence-Lotto) same time 8. Denis Menchov (Russia/Rabobank) same time 9. Christian Vande Velde (US/Garmin - Chipotle) same time 10. Bernhard Kohl (Austria/Gerolsteiner) same time
118. David Millar (GB/Garmin) +38min
Overall standings (after 17 stages):
1. Carlos Sastre (Spa/CSC) 74hrs 39min 3sec 2. Frank Schleck (Lux/CSC) +1min 24sec 3. Bernhard Kohl (Aut/GST) +1min 33sec 4. Cadel Evans (Aus/SIL) +1 min 34 sec 5. Denis Menchov (Rus/RAB) +2min 39sec 6. Christian Vandevelde (US/GAR) +4min 41sec 7. Alejandro Valverde (Spa/GCE) + 5min 35sec 8. Samuel Sanchez (Spa/EUS) + 5mins 52sec 9. Tadej Valjavec (Slovenia/AG2R) +8min 10sec 10. Vladimir Efimkin (Russia / AG2R ) +8min 24sec
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