Frank Schleck wrestled the yellow jersey from the grip of Cadel Evans as the race favourite suffered badly on the summit finish to Prato Nevoso in the Tour de France.
CSC's Schleck, who trailed Evans by one second going into the 15th stage from Embrun, takes a seven-second lead in the general classification from Bernhard Kohl, who headed home the chasing pack behind the breakaway group.
Kohl, of Gerolsteiner, finished fifth in the stage ahead of Schleck, ninth, and the Austrian has a one-second advantage over Evans, who drops to third overall.
As Evans toiled in yellow, his fellow Australian Simon Gerrans rode the perfect ascent up Prato Nevoso to outfox his fellow escapees and win the 183km stage by three seconds from Egoi Martinez.
The 28-year-old Credit Agricole rider sat on the wheel of Danny Pate and Martinez, and kicked away in the final metres.
Martinez, King of the Mountains at the 2006 Vuelta a Espana and a better climber, appeared to be in the box seat when the trio entered the last 300m of the 11.1km climb to the Italian ski station, but he could not respond when Gerrans made his move.
The escapees benefited from several crashes in the peloton, most notably to third-placed Christian Vandevelde, and 2006 Tour winner Oscar Pereiro, who was forced to retire with a broken femur and shoulder.