Casey Stoner's charge towards the MotoGP title continued on Sunday when the Australian dominated the San Marino Grand Prix from start to finish.

The Ducati rider's eighth victory of the season, his third consecutive win, gave him an 85-point lead over Italy's [Images] Valentino Rossi [Images], who retired after his Yamaha's new engine suffered mechanical failure on the fifth lap.

The result makes it possible for Stoner to clinch the championship at the Portuguese Grand Prix at Estoril on September 6 with four races to spare but the 21-year-old said he would not let that thought influence his approach.

"Already the title was close before this race and I still want to go out and win races because this is why we race," he said on Italian television.

"The championship is a bonus at the end but we have many races until then so I want to try to win as many as possible.

"Today again was a great day, I didn't expect to be so competitive as we struggled a little bit at the weekend. The team worked very hard in the night time and we were able to come out with a good setting for the race."

Australia's Chris Vermeulen came in second on a Suzuki to consolidate fourth place in the standings on 144 points.

He praised Stoner and his team.

"I tried my hardest and I got close to him at one point but I didn't know how I'd get past the Ducati and at the end I wasn't even close enough to tag him," Vermeulen said.

Fellow Suzuki rider John Hopkins of the United States, who shared fourth place in the table with Vermeulen before the race, finished third.

HEAVY CRASH

Italy's Marco Melandri came back from a neck injury that kept him out of the Czech Grand Prix and a heavy crash in practice on Saturday to finish fourth after starting 12th on the grid.

Loris Capirossi also did well to charge up to fifth place from 13th on the starting line.

World champion Nicky Hayden, who started on the front row, came 13th after being involved in a crash on the first corner that knocked out his Honda team mate Dani Pedrosa.

Pedrosa remains third in the standings with 168 points.

The exit of Rossi was a massive disappointment for the 57,000 fans at the Misano track, which is in Italy, not San Marino, near the town of Tavullia where he grew up.

"Yamaha have to change something," Rossi told La Gazzetta dello Sport's website. "I prefer to do something else than race if I have to race like this.

"Ducati and Stoner deserve to win this world championship and I take my hat off to them," added the Italian, who has had problems with tyres for much of the season and has come under fire in Italy recently because of a tax-evasion probe.

"But I don't think anyone likes this situation with the tyres, not even Ducati. The races are becoming ugly, there is no battle any more. We are becoming like Formula One."

By winning on Sunday, Stoner ended the dominance on his home soil of five-times premium class world champion Rossi, who has won the last six Italian Grands Prix.

The Grand Prix at Misano, which last hosted premier class racing in 1993, is a new addition to the MotoGP schedule. Although it is in Italy, organisers named it after the principality of San Marino to distinguish the race from the Italian Grand Prix at Mugello.