Lorenzo had to finish ninth or better at Sepang to wrap up the championship with his closest rival Dani Pedrosa sidelined through injury.
It was defending champion Rossi's first victory since the opening race of the season in Qatar and he turned on the style on one of his favorite circuits to edge out Italian compatriot Andrea Dovizioso on a Honda who finished second.
The 31-year-old Rossi, who will join Ducati next season, started from the second row and even slipped back down the field before powering through the pack in spectacular style.
Casey Stoner, who was bidding for his third straight victory for Ducati, crashed out on the first lap as Dovizioso and Lorenzo initially led the way.
But Rossi caught up the leaders by halfway of the 20-lap race and took the lead as he first passed Lorenzo and then Dovizioso.
CNN
