World championship leader Jorge Lorenzo won the San Marino MotoGP to extend his lead in the standings on Sunday while his nearest challenger and fellow Spaniard Dani Pedrosa crashed early in the race in Misano.
Honda rider Pedrosa was involved in a collision with compatriot Hector Barbera and both riders crashed out.
Italy's Valentino Rossi was second, just ahead of Alvaro Bautista. Australian world champion Casey Stoner, third in the overall standings, is out of action after undergoing surgery on his ankle in August.
The race got off to a troubled start due to problems with Karel Abraham's bike while Pedrosa, who took pole position on Saturday, had to start from the back after wheeling his bike into the pits to restart it.
Pedrosa was moving up through the field when he and Barbera collided in a potentially dangerous incident but the following bikes managed to avoid the two fallen riders.
Mattia Pasini, Cal Crutchlow and Abraham also tumbled out in the opening laps.
Lorenzo charged away at the front to move 38 points ahead of Pedrosa, with five races left.