Australia's world championship leader Casey Stoner led from the end of the first lap and was never challenged en route to claiming his sixth MotoGP win this season at the US Grand Prix on Sunday.

The Ducati rider, 21, who was the pole-setter and was fastest in all three practice sessions, extended his lead in the standings to 44 points over Valentino Rossi after clocking victory in 44 minutes 20.325 seconds at the Laguna Seca Raceway.

Compatriot Chris Vermeulen finished second on his Suzuki in 44:30.190. Marco Melandri, of Italy, who rode with a severely sprained ankle, finished third for Honda in 44:45.966. Rossi placed fourth for Yamaha in 44:50.989.

"We got a reasonable start and got past Dani (Pedrosa) at the end of the first lap," said Stoner of the 32-lap contest.

"After that, I just rode my own race for the rest of the day. It was unbelievable."

Stoner averaged 156.323kph during his dominating ride in which he ended a run of 12 MotoGP races in which the pole-setter had failed to win.

Stoner's victory further extended the Australian's lead after the 11th race of the 18-event calendar. Stoner has 221 points, followed by Rossi with 177 points and Pedrosa with 155 points.

Reigning world champion Nicky Hayden of the United States, seeking his third straight win in the race, bumped with compatriot John Hopkins on the second lap, swerved off course but remained in the event for several more laps before withdrawing.

Races were not held in the 125cc and 250cc classes.

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