Even if Vettel maintains his lead in the first stint, he's up against the strategic genius of Ross Brawn. RBR's strategies have been lacking this season, while Brawn's (namely Button's) strategies have been spot-on. It's very possible that Button will somehow leap-frog Vettel in the pits.
Good factors for Vettel are that he is starting from pole, on the clean side of a notoriously green track, with a highly competitive car.