Sastre went clear on the final ascent to take the last of three Alpine stages, which started at Embrun and covered 210.5 kilometers (131 miles), including the climbs of the Galibier and the Croix de Fer.
Today's stage is one of the most celebrated mountain tests in the tour and includes 21 hairpin bends on the final ascent. It was the last chance for climbing specialists to improve their overall standing in this year's race.
The three-week race ends in Paris in four days.
NVDL: Now it comes down to Saturday's timetrial.