MotoGP world champion Casey Stoner secured his third successive victory after winning a rain-soaked German Grand Prix today.

The Australian overcame sickness as well as the poor conditions to finish 3.708 seconds ahead of former champion Valentino Rossi of Italy, who regained the overall lead in the standings from Spaniard Dani Pedrosa who bowed out early in the race.

Australian Chris Vermeulen clinched third spot, 14.002 seconds behind Stoner after a tight race to the line with San Marino's Alex de Angelis.

"I've been feeling sick since yesterday morning," a groggy-looking Stoner said. "I was struggling with my concentration levels and it wasn't getting any better today.

"Those conditions were very, very hard. I was losing it and aquaplaning in a lot of places so I was lucky to come out of that one on the bike, let alone win the race."

Stoner started in pole position but was left trailing in the opening stages by Pedrosa.

Pedrosa appeared to make light work of the wet track to open up a gap of more than six seconds over the chasing pack before sliding off at the start of the sixth lap.

Stoner capitalised to retake the lead and hold off Rossi for the remaining 25 laps.

With eight races remaining, Rossi leads Pedrosa by 16 points with Stoner third, a further four points behind.