Andy Schleck attacked with panache on the Col d’Izoard before claiming victory on the Col du Galibier, the highest-ever finish in the Tour de France, but Thomas Voeckler fought bravely on the final climb to keep the yellow jersey by just 15 seconds.
Schleck outsmarted his general classification rivals with an early bid for glory with more than 60km remaining.
The Leopard-Trek rider held a lead of more than four minutes at the foot of the Col du Galibier, ploughing a lone path up the third hors categorie climb of the day with Voeckler rallying to finish two minutes, 21 seconds back in fifth to cling on to the yellow jersey with just three stages remaining.
Frank Schleck produced a late burst to claim second on the stage to lie third overall, one minute, eight seconds back, while Cadel Evans, third on the day, is a further four seconds adrift in the general classification with one day left in the Alps.
Mark Cavendish finished outside the time limit in a group of 88 riders and was subsequently docked 20 points, reducing his green jersey lead over Jose Joaquin Rojas, who made the cut-off, to just 15 points.
Andy Schleck lost more than a minute to Evans, defending champion Alberto Contador and Samuel Sanchez on stage 16, before labelling the final descent of the Côte de Pramartino on stage 17 as ‘fatally dangerous’.
But the Luxembourg rider, second behind Contador in both 2009 and 2010, answered his critics with a bold attack on the Izoard.
The yellow jersey group was happy to let Schleck go, with the 26-year-old quickly building a lead of more than two minutes at the 2,360m summit.
Leopard-Trek, in a tactical masterstroke, put Maxime Monfort in the day’s 19-man break and Schleck joined forces with the Belgian before forming part of a five-strong group that also included Ag2r La Mondiale’s Nicolas Roche, just leaving stage leader Maxim Iglinskiy out front.
Schleck extended his advantage to more than three minutes at Briancon, the highest city in the European Union, to become the virtual yellow jersey, before catching Iglinskiy on the false flat to the ski resort of Serre Chevalier.
Despite SaxoBank increasing the pace at the front of the peloton, the lead group, with Monfort setting a brutal pace into a headwind, continued to extend its lead with just 20km remaining.
The 2011 race celebrates 100 years since the Tour de France first crossed the Col du Galibier, with the route taking on the fabled mountain pass twice, first with today’s summit finish before climbing the harder northern side en-route to Alpe d’Huez on Friday.
Schleck turned on to the Galibier with only Iglinskiy on his wheel but soon burnt off the Kazakhstan rider, while, back in the chase group, Evans pushed to the front in an effort to reduce the deficit.
Evans’ reaction quickly knocked 30 seconds off Schleck’s lead as the Australian, second overall at the start of the day, fought to save his Tour de France, going on to reduce the deficit to three minutes, 15 seconds with 5km to the summit.
Contador cracked in the closing kilometres and was quickly distanced by the chasing group, eventually losing nearly four minutes to end his Tour de France title defence, while Schleck began to suffer as the gradient reared up on the final passage to the summit.
Meanwhile, Voeckler, aided once again by domestique Pierre Rolland, continued his charge and, with the clock ticking after Schleck crossed the line, defended his surprise maillot jaune for the tenth day running ahead of Friday’s Alpine finale on the 21 hairpins of Alpe d’Huez.
1. Andy Schleck (LUX/LeopardTrek) 6h 07m 56s
2. Frank Schleck (LUX/Leopard Trek) +2’07”
3. Cadel Evans (AUS/BMC Racing) +2’15”
4. Ivan Basso (ITA/Liquigas-Cannondale) +2’18”
5. Thomas Voeckler (FRA/Euskaltel-Euskadi) +2’21”
6. Pierre Rolland (FRA/Euskaltel-Euskadi) +2’27”
7. Damiano Cunego (ITA/Lampre-ISD) +2’33”
8. Rein Taaramae (EST/Cofidis) +3’22”
9. Tom Danielson (USA/Garmin-Cervelo) +3’25”
10. Ryder Hesjedal (CAN/Garmin-Cervelo) +3’31”
1. Thomas Voeckler (FRA/Europcar) 79h 34m 06s
2. Andy Schleck (LUX/Leopard-Trek) +15”
3. Frank Schleck (LUX/Leopard-Trek) +1’08”
4. Cadel Evans (AUS/BMC Racing) +1’12”
5. Damiano Cunego (ITA/Lampre-ISD) +3’46”
6. Ivan Basso (ITA/Liquigas-Cannondale) +3’46”
7. Alberto Contador (SPA/SaxoBank) +4’44”
8. Samuel Sanchez (SPA/Euskaltel-Euskadi) +5’20”
9. Tom Danielson (USA/Garmin-Cervelo) +7’08”
10. Jean-Christophe Peraud (FRA/Agr2 La Mondiale) +9’27”