Casey Stoner rode to his fourth victory of the 2009 MotoGP season, and second in a row, with an incredible wet weather ride at Sepang in Malaysia on Sunday.

A heavy tropical storm delayed the race start and meant the 17-rider field would be riding in wet conditions for the first time all weekend.

Starting third - after Jorge Lorenzo was moved to the back of the grid - Stoner got a poor start, but salved the situation with some smart moves through the right-left first turns, which he emerged in fourth position.

The Ducati star rode around his rivals to lead by the end of first lap, then appeared to almost effortlessly pull over 17 seconds ahead, before backing off slightly as the track began to dry to win by 14.666sec.

"It was the same conditions for everyone today. None of us had tested in the wet here for quite a long time," said Stoner. "I was a bit tentative and didn't get a good start, but slotted into fourth coming out of turn two and was pretty happy with that.

"When I took the lead I thought I'd test the track for a few laps and I didn't expect to pull the gap I did.

"After that I just decided to keep going for at least half race distance and by the time I got a gap I was happy with I backed off because the track was starting to dry a bit. The tyres were actually in a lot better condition than I thought, but they were getting a bit 'greasy'," he explained.

Having missed three rounds to seek treatment for mystery fatigue problems, Stoner has now finished a near-perfect 2nd, 1st and 1st in the three races since his return.

"We can't ask for anything more," declared the 2007 world champion. "These last three races been have been close to perfect, we were only one result off that in Portugal and that is a difficult circuit for us anyway.

"A big thanks to my team, everyone that has supported me and all the doctors that have helped me out.

"I'm really looking forward to Valencia now, a circuit I really enjoy," he continued. "We're really strong now and I can only see us getting stronger from here, which is great news for next season."

Whilst Stoner celebrated victory, third for Valentino Rossi gave the Italian his ninth world championship.

"I want to congratulate Valentino because to win nine world championships is an incredible achievement," said Stoner. "I'm sure that if we continue to work like this ourselves we can put up a much stronger challenge next time."

Stoner will start the Valencia season finale third in the championship and 11 points ahead of Dani Pedrosa (Honda), who was second in Sunday's race.

Despite his mid-season break, Stoner still has a slim chance of snatching second from Jorge Lorenzo, although Stoner would need to win at Valencia with Lorenzo failing to score.

Rossi has won six races this season, with Lorenzo and Stoner tied on four victories from the 16 rounds so far held.

Stoner's team-mate Nicky Hayden also produced a competitive display on Sunday, claiming his fourth top six finish of the year with fifth position.

"We'll take a top five, that'll work for us," said Hayden. "I was quite excited when it started to rain because I've been on the pace with this bike in the wet this year and I felt I could do something special. Unfortunately I struggled a lot on the brakes in the beginning and a lot of guys came past."

Seventh at the end of lap one, the American was involved in a series of exciting battles, passing Loris Capirossi and Toni Elias and doing his best to hold off title contenders Rossi and Lorenzo.

"I had a lot of fun passing and fighting with people, trying to close down the gap to the lead group, but I was just missing a little bit to really go with Rossi and Lorenzo and try to fight for the podium," he said.

"When Vermeulen [sixth] came I knew he was a rain specialist so I pushed hard to make sure he didn't see a crack in the door and think he could push it open. I've been fourth here five times so I'm only one spot off my mark!

"After Phillip Island it seems every time we try to get something going we have huge bad luck but I'm thankful I have a team who keep working and never give up - we're trying to build something here together and we're making progress. Even this weekend we were consistently up near the top.

"I have to say congratulations to Casey and Valentino. It wasn't a terrible day for us either but now we go to Valencia and try to build on it again," he concluded.

"That was a really wonderful and unique day, for the way the conditions changed so quickly and the way our team reacted to it, and for the positive result for both of our riders," said Ducati MotoGP project director Livio Suppo, whose team was blasted for its ill-fated reaction to damp conditions at Donington park earlier this year.

"Casey produced something extraordinary, dominating from the first to the final lap, whilst Nicky battled hard from the start and brought home an important fifth place that shows how well we have worked both at the track and back at the factory throughout the year.

"It is a season that saw Casey make a great start before going through some difficulties and then coming back in style, whilst Nicky had a tough start himself but he has made constant progress and he is finishing it in a positive way that we hope carries through to next year."