Australia's world championship leader Casey Stoner stormed to his sixth victory of the season in the MotoGP race at the Czech Grand Prix here Sunday. Stoner, winning here for the first time since 2007 the same year he went on to win the world crown, beat his Honda Repsol teammate Andrea Dovizioso of Italy by 6.532 seconds. Italy's Marco Simoncelli on another Honda came in third, while defending world champion Jorge Lorenzo lost more points to the Australian in finishing fourth. Spanish pole-sitter Dani Pedrosa crashed out on lap three, followed by Britain's Cal Crutchlow, Czech Karel Abraham and Spain's Alvaro Bautista who also failed to finish after crashes. Italian Suter rider Andrea Iannone won the Moto2 race. Spain's Marc Marquez was second and Stefan Bradl of Germany third. Germany's Sandro Cortese of Aprilia edged France's Johann Zarco narrowly to secure the first victory of his career in the 125cc race.