Marlboro Ducati rider Casey Stoner continued his fine form since returning from illness with second place, with Repsol Honda rider Dani Pedrosa in third and Rossi in fourth.
A fourth-place finish on Sunday will be enough for Rossi to take his seventh premier-class world championship even if Lorenzo wins, and the Italian was in relaxed mood as he lapped 0.684 seconds slower than his young rival.