Marquez was joined on the podium by VR46 Racing riders Fabio Di Giannantonio and Franco Morbidelli, with Luca Marini finishing fourth to give Honda a rare boost.
An incident-packed opening lap saw three riders crash out in separate incidents, with Yamaha's Fabio Quartararo the biggest culprit when he was involved in a collision on turn one.
Gresini Racing's Alex Marquez, second in the championship, finished eighth while Marc's teammate Francesco Bagnaia, third in the table, came a lowly 13th.