Italian Andrea Dovizioso won the San Marino Grand Prix for Ducati while reigning world champion Marc Marquez finished second to increase his MotoGP championship lead to 67 points.
Starting fourth in Sunday's race, Dovizioso quickly moved up the grid then passed pole sitter Jorge Lorenzo to take the lead early and wasn't challenged the rest of the way.
It was Dovizioso's third win this season and the 11th of his MotoGP career.
"We did everything perfectly," said Dovizioso, who had started in fourth place and was leading after six laps. His winning margin was 2.822 seconds.
"That was the only way to win today because Jorge was very strong and beating Marc was very difficult."
Australian Jack Miller, who had lined up in second place at the start on a non-factory Pramac Ducati crashed out early on while fourth.
Local favourite Valentino Rossi managed only a distant seventh for Yamaha and lost second place overall to Dovizioso who now has 154 points to Spaniard Marquez's 221 with six races remaining. Rossi has 151.
Lorenzo also crashed out, on the penultimate lap, at the Marco Simoncelli circuit on Italy's Adriatic coast, while heading for a Ducati one-two finish. That lifted Britain's Cal Crutchlow to third as the leading non-factory finisher on an LCR-Honda.
Italian Moto2 rider Romano Fenati was banned for two races after leaning over on the straight and grabbing the brake lever on rival Stefano Manzi's bike following an earlier clash.
Stewards ruled he had "deliberately attempted to cause danger to another rider by interfering with his machine whilst on track".
Fenati was immediately shown the black flag, disqualifying him from the race, but Crutchlow felt the rider had got off lightly.
"I think he should never race a motorcycle again," Crutchlow told reporters.
"He should have walked back to the garage and his team should have just kicked him straight out the back."
