A fairy tale season came to a dramatic conclusion for Casey Stoner, who secured his first MotoGP world championship with sixth place in the Japanese Grand Prix in Motegi.

A nerveless Stoner, 21, overcame rain, a chaotic mid-race pitstop and the challenge of the great Valentino Rossi to claim the title he has dreamed of since the age of three.

Stoner joins Wayne Gardner and Mick Doohan as the only the third Australian to win the MotoGP crown.

The race was won by Stoner's Ducati teammate Loris Capirossi who scored his first win of the season.

Beaming his trademark smile, Stoner was almost lost for words to sum up the realisation of his dream.

"It's just very nice, I really don't know what to say, it's a little overwhelming, I have dreamt about this since I was a kid watching the races on television," he said.

"And it is great feeling to win the championship ahead of Valentino Rossi, who is one of my heroes."

Rossi paid tribute to his young rival who has never wilted under the season-long pressure from the Italian.

"I want to congratulate Casey on becoming world champion, he's a great rival, and I hope we can continue this rivalry into the future," Rossi said.

Stoner's title assault at Motegi, which appeared to falter when he qualified ninth for the race, was revived midway through the 24-lap race when Rossi slowed with front tyre problems.

Earlier Stoner had surged to the lead briefly on lap four, only to drop to eighth after his lap 15 pitstop.

The race had started on a wet track, making strategy and pitstop timing crucial.

No sooner had Rossi moved into second place, thus putting Stoner's title claim in doubt, that the great Italian rider was slowed with front tyre problems.

He dropped to 13th with another pitstop, leaving Stoner to concentrate on claiming the title over the final eight laps.

"The first part of the race on wet tyres I was comfortable with the pace and I knew they would lose grip as the track dried out," Stoner said.

"And sure enough, the tyres destroyed themselves so I came in for my spare bike fitted with slick tyres.

"I wasn't sure what to do because I didn't know what the other riders were doing because of the conditions and then my team gave me the signal to make the pitstop.

"And then when I saw that Valentino was having troubles I started to relax and just concentrate on finishing the race.

"I don't really remember too much of the last two laps. But I don't think there can be a better feeling than winning the world championship."

Fellow Australians Ant West and Chris Vermeulen had mixed fortunes.

West made blinding start and led for two laps but was penalised for a jump start and dropped back to 14th.

West made a remarkable comeback in slippery conditions to finish seventh while Vermeulen, who struggled in qualifying, finished in 11th, more than one minute behind Stoner.

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