France in spectacular fashion on Thursday when a bold attack earned him an impressive win in the 18th stage.
The Luxembourg rider, runner-up in the last two editions of the Tour, jumped from the pack in the penultimate climb of the stage, a 200.5-km effort from Pinerolo, Italy.
The Leopard-Trek rider took the day's laurels ahead of his brother Frank, who finished 2:07 behind, according to provisional results.
Australian Cadel Evans finished third eight seconds further back as he managed to salvage his chances thanks to a terrific effort in the final ascent that dealt a fatal blow to Spain's three-times champion Alberto Contador.
France's Thomas Voeckler retained the yellow jersey as he ended the stage in fifth place and leads Andy Schleck by 15 seconds with two competitive stages left.
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Frank Schleck lies third 1:08 off the pace with Evans in fourth place four seconds further back.
Schleck attacked with 60 km left in the ascent to the Col d'Izoard, building a three-minute lead over the favourites' group after joining a few breakaway riders.
With the help of team mate Maxime Monfort, Schleck's lead grew to 3:45 in the valley leading to the foot of the Col du Galibier, despite strong headwinds.
The gap increased to 4:30 in the first slopes of the 22.8-km ascent to the Col du Galibier at an average gradient of 4.9 percent.
Contador, who suffered from knee pains again, was unable to up the pace in the final climb as the favourites played a waiting game that cost them dearly.
Evans finally decided to take the matter into his own hands as he accelerated with nine kilometres remaining.
Schleck's lead dropped but an exhausted Contador eventually crossed the line with a 3:49 deficit.
