Jorge Lorenzo has slashed team-mate Valentino Rossi's championship lead from 30 to 18 points with his fourth victory of the season in Sunday's Portuguese Grand Prix at Estoril.
The result meant that Yamaha lifted the 2009 MotoGP Constructors' title, and Fiat Yamaha the Teams' title, with three rounds still to go.
Repsol Honda's Dani Pedrosa
made his usual fast start to take the holeshot at turn one, but Lorenzo was quickly ahead of his fellow Spaniard and several bikelengths clear by end of the first lap. Lorenzo remained in front to the chequered flag.
Casey Stoner, making his MotoGP comeback after missing three rounds due to fatigue problems, had dropped from third to fifth at turn one, before muscling past Tech 3's Colin Edwards
to finish the first lap in Rossi's wheeltracks.
The Ducati star attempted to outbrake Rossi at turn one next time around. The Italian held firm, but Stoner responded by sticking alongside the #46 through the kink and slotting into third at the following turn.
Riding as wild as ever and eager to prove a point on his comeback, Stoner brushed Pedrosa aside to take second place just one lap later, with Lorenzo the only rider still ahead of the Australian.
But the #99, who took his first MotoGP victory at Estoril last season and hadn't won from pole since, broke the lap record as early as lap three and was able to more than match Stoner's challenge.
By the halfway point of the 28 laps Lorenzo had established a 2.3sec lead over Stoner, with Pedrosa 1.3sec further back and a clearly off-form Rossi already 7.7sec from his Fiat Yamaha team-mate and out of victory contention.
Despite his undiminished speed, question marks still remained about whether Stoner would last the race distance - after fading backwards in the five rounds before his mid-season withdraw.