Championship contender Jorge Lorenzo topped the timesheets during Friday's first practice session as the FIM MotoGP World Championship hit Sepang.
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.