Nieto extended his 250cc championship lead

But the championship leader almost left it too late.

After 17 laps, Ukawa held the lead with Rossi trapped in third, behind his compatriot Biaggi.

And with Biaggi holding Rossi up, Ukawa was threatening to pull clear into a winning lead.

However, Rossi managed to dive past his countryman on lap 18 and immediately closed in on his Japanese team-mate.

The Italian slipped past Ukawa just as the race was approaching the crucial two-thirds distance mark to guarantee his third victory in this season's four Grands Prix.

"The rainfall on the first part of the track made it difficult and towards the end I pushed to get into first, and was lucky to be there when the race was stopped," said Rossi.

Ukawa, however, was happy enough with his second place.

"It was a difficult race today because the conditions did not help us," he said.

"But I was happy because the machine worked very well and the tyres as well.

"After all, second place is not so bad, and it is good for the championship so I'm happy."

Yamaha rider Carlos Checa, who had started second on the grid, fell on lap nine.

Spaniard Fonsi Nieto claimed his second successive 250cc race of the season, winning a fierce battle with Marco Melandri to lead the world championship on 69 points.

Aprilia completed a double when Lucio Cecchinello took the 125cc category, with world championship leader Arnaud Vincent fourth.