Andy Schleck made his claim for Tour de France victory with a solo surge to win at the highest summit finish in the race's history today, but Thomas Voeckler retained the yellow jersey for a 10th day with another resilient performance.
The 200.5-kilometre 18th stage from Pinerolo returned to France, finishing at Galibier Serre-Chevalier - at an altitude of 2,645metres - and presented an opportunity for the overall favourites to attack.
Andy Schleck (Leopard Trek), runner-up to Alberto Contador in each of the last two years, did just that but could not end Voeckler's stint in the yellow jersey.
The 26-year-old from Luxembourg began the day two minutes 36 seconds behind Frenchman Voeckler (Europcar) and attacked on the 14.1km Col d'Izoard to distance himself from the yellow jersey group, which included the other overall favourites.
He forged forward, catching the remnants of the day's breakaway before his high tempo up the hors categorie (beyond category) Col du Galibier saw him solo to a third Tour stage win.
Frank Schleck (Leopard Trek) was second, 2mins 07secs behind his brother, and Cadel Evans (BMC Racing) was 2:15 behind, while Voeckler was 2:21 adrift in fifth to stay in the maillot jaune by 15 seconds from Andy Schleck.
Defending champion Contador (Saxo Bank-SunGard) was not so lucky, finishing 3:50 down in 15th place and now sits seventh, 4:44 behind Voeckler with three days of racing remaining.
Prior to the finale, the 23km ascent of the Col du Galibier, the peloton had to negotiate two other hors categorie climbs.
A 16-man break was established shortly before the day's intermediate sprint, which took place after 46.5km and saw none of the leading green jersey contenders take points.
Mark Cavendish (HTC-Highroad) was merely seeking to survive today and was dropped on the day's opening climb, the 23.7km Col Agnel.
Maxim Iglinskiy (Astana) led over the Col Agnel but fell back again before attacking for a second time on the day's second major climb.
Behind him, Andy Schleck also made his move midway up the Col d'Izoard, quickly establishing a gap between himself and the yellow jersey group, which opted not to respond as 60km of the stage remained.
Andy Schleck reached the summit more than two minutes before Voeckler's group, but required assistance on the descent and followed the line taken by team-mate Maxime Monfort, who had been involved in the day's early breakaway.
Rigoberto Uran (Team Sky), wearing the best young rider's white jersey, crashed on the descent of the Col d'Izoard, losing valuable seconds, but caught up with the yellow jersey group with assistance from team-mates Xabier Zandio and Geraint Thomas.
Contador required a bike change around 40km from the finish, as up ahead Andy Schleck and Monfort caught Iglinskiy and three other riders - Nicolas Roche (Ag2r La Mondiale), Dries Devenyns (QuickStep) and Egor Silin (Katusha) - on the descent through Briancon to form a six-man leading group.
The six leaders began the climb of the Col du Galibier, which begins gently, with an advantage of more than three minutes over Voeckler and company.
With 17.5km remaining Andy Schleck accelerated again, with Roche, Iglinskiy and Silin following him.
Silin soon fell away to leave three in the leading group.
Behind them, as the lead increased to four minutes, Contador moved to the front of the yellow jersey group, with Evans, Frank Schleck and Ivan Basso (Liquigas) also present.
The yellow jersey group hesitated, allowing others to reel them in, with around 15km of the ascent still to go and with no-one apparently willing to take responsibility to lead the chase.
As the pace set by Andy Schleck saw Roche fall back, Evans attacked behind, stretching the peloton into a long line.
With 7.8km left, Andy Schleck burst free of Iglinskiy, going alone, while Evans continued to grind away at the front of the peloton.
The Australian was towing along Voeckler and the other leading riders, with Contador around 10th in the group, but Samuel Sanchez (Euskaltel-Euskadi) lost contact and faded.
With 5km to go Andy Schleck had an advantage of 3:15, with Evans still leading the pursuit, but with 3km to go on the climb, Contador had to fight to stay with Evans, Voeckler - supported by Pierre Rolland - Frank Schleck, Basso and Damiano Cunego (Lampre-ISD) before being dropped moments later.
Andy Schleck suffered in the finale, almost coming to a halt with 200m to go, before celebrating victory.
But the maillot jaune proved elusive as Voeckler dug deep into his energy reserves to retain the race lead.
Tomorrow's 109.5km 19th stage from Mondane Valfrejus to Alpe-d'Huez represents another opportunity for the overall favourites - and perhaps the last chance for the Schleck brothers to gain time on their rivals, given their inferior time-trial ability.
Saturday's penultimate stage is a 42.5km time-trial in Grenoble.