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.

Fortunately, although the 2007 world champion wasn't able to threaten Lorenzo, he comfortably contained the riders behind him to claim his sixth podium of the season and first since Assen on June 27.

Lorenzo - riding with an astronaut helmet and dressed, like Rossi, in a special silver and white Fiat Punto livery - took victory by 6.294 sec over a beaming Stoner, while Pedrosa claimed his eighth podium of the year with third, 9.9sec from Lorenzo.

After victory, Lorenzo performed a mock moonwalk before planting his Lorenzo's Land flag into the Estoril gravel.

Rossi's 100th grand prix for Yamaha proved to be a forgettable event, with the reigning six time MotoGP world champion finishing off the podium for the first time ever as a MotoGP rider at Estoril - and shrugging his shoulders after returning to the pits.

Crossing the finish line 23.428sec behind Lorenzo, Rossi's world championship lead has now dropped to less than one race win (25 points) for the first time since the German Grand Prix on July 19.

Edwards finished where he had started, in fifth, while 2006 Estoril winner Toni Elias charged from 13th on the grid to sixth for San Carlo Honda Gresini, after battling furiously to hold off factory Honda rider Andrea Dovizioso in the closing stages.

Mika Kallio failed to finish on his return to the Pramac Ducati team, crashing out through the long final turn early in the race, leaving Nicky Hayden to finish as the second best Desmosedici behind team-mate Stoner in eighth.

James Toseland finished in ninth for Tech 3, with Chris Vermeulen the only Rizla Suzuki rider to finish - in tenth - after team-mate Loris Capirossi, sixth on lap one, retired with engine problems.

Alex de Angelis also suffered mechanical misery, leaving Randy de Puniet (LCR Honda), Marco Melandri (Hayate), Niccolo Canepa (Pramac Ducati) and Gabor Talmacsi (Scot Honda) to complete the finishers.

Round 15 of the 2009 MotoGP World Championship will take place at Phillip Island, Australia, on October 18 - Stoner's home event.

Portuguese Grand Prix:

1. Lorenzo
2. Stoner
3. Pedrosa
4. Rossi
5. Edwards
6. Elias
7. Dovizioso
8. Hayden
9. Toseland
10. Vermeulen
11. de Puniet
12. Melandri
13. Canepa
14. Talmacsi