Pole sitter Cal Crutchlow wiped out before a three-rider crash involving then points leader Andrea Dovizioso, Jorge Lorenzo and Dani Pedrosa.

That left Marquez free to increase his lead and never be challenged as the four-time MotoGP champion cruised to his 37th career victory in the top category.

"Dani was the fastest, but a race is not only about being the fastest,'' Marquez said. "You have to overtake, be aggressive in certain moments. I hope they are OK, but I won't lie, [it means] more points for me.''

Marquez steered his Honda across the finish line in 41 minutes, 39.678 seconds, more than five seconds before Johann Zarco, who finished second.

Andrea Iannone completed the podium.

Marquez leads the competition with 70 points after four races. Zarco is second with 58, followed by Maverick Vinales with 50.

Lorenzo Baldassarri won the Moto2 race ahead of Miguel Oliveira and Francesco Bagnaia, who leads the category with 73 points. Baldassarri is second with 64.

In Moto3, Philipp Oettl got his first career win after edging Marco Bezzecchi at the line. Bezzecchi leads the standings with 63 points, ahead of Jorge Martin with 55.