Father-to-be Casey Stoner has a firm grip on the world MotoGP championship after securing his sixth win of the season.

Stoner beat his Honda teammate Andrea Dovizioso of Italy by 6.532 seconds on Sunday to claim victory in the Czech Grand Prix at Brno for the first time since 2007, the year he won his one world title.

It capped another good weekend for the 25-year-old Australian, who had revealed he and his wife Adriana are expecting their first child.

Stoner took the lead after Spanish pole-sitter Dani Pedrosa crashed out from first place on lap three and kept building his advantage until easing slightly on the last few laps.

Italy's Marco Simoncelli on another Honda came third while defending world champion Jorge Lorenzo lost more points to Stoner in finishing fourth.

With seven races to go in the season, Stoner now has a comfortable overall lead with 218 points ahead of Lorenzo (186) and Dovizioso (163).

"I had a really tough battle with Andrea (Dovizioso) in the early laps but once I got past him I realised the bike had enough speed," said Stoner, after winning his 29th MotoGP.

"After a tough weekend it's really satisfying to win here," he added after finishing in fine sunny weather that helped dry the circuit after Saturday's rain.

Dovizioso said he was pleased with his result and his "really competitive team."

"I made a really good start, I tried to cut Casey but I made a mistake," he said.

Simoncelli was also content to be on the podium.

"We as a team were confident of achieving a podium position this season and I am really happy to have got my first one," said Simoncelli.

Lorenzo took the lead briefly in lap one but then he gave in to pressure from Dovizioso and Simoncelli, and he had to fight hard to shake off Yamaha's US rider Ben Spies, who took the fifth place.

Italian Ducati rider Valentino Rossi came in sixth, failing to extend his record of five MotoGP victories on Brno's undulating 5.403-kilometre circuit about 180 kilometres southeast of the Czech capital Prague.