The race was red-flagged twice, the first time after Pedro Acosta's bike cut out and Marquez made contact with him, with his Ducati-Gresini destroyed in a horrific crash.

On the first corner after the restart, French rider Johann Zarco crashed and the race was red-flagged again, and restarted with 12 laps remaining.

Acosta started on pole and was out in front until Di Giannantonio snatched the lead with two laps remaining.

Joan Mir and Fermin Aldeguer also edged ahead of Acosta, who then came to grief shortly before the end after being wiped out by Ai Ogura, who was hit with a time penalty and dropped to ninth.

Race organisers said Mir, who finished second, and several other riders are under investigation for tyre pressure regulations. Fermin Aldeguer completed the podium.

Overall leader Marco Bezzecchi struggled all weekend but was able to extend his advantage after his closest contender Jorge Martin suffered his fifth crash of the weekend.

Raul Fernandez took out Martin after trying an aggressive move down the inside while they were challenging for the lead, leaving Bezzecchi, who finished fifth, 13 points ahead.

Di Giannantonio hurt his hand in the first terrifying crash when the Italian was hit by a wheel from Marquez's ruined bike, but the VR46 man recovered to claim his first MotoGP win in three years.

"I'm so happy. But first of all I was really worried about all the riders who crashed," said Di Giannantonio.

"Today has not been an easy day for everybody. I really hope that Alex (Marquez) is fine. We've been really lucky.

"We know that our sport is amazing. We try to give an amazing show, we are humans, we are in danger."

Di Giannantonio's victory moved him up to third overall on 116 points, followed by Acosta on 92.

Marquez, who triumphed at last year's Catalan Grand Prix and also won the sprint on Saturday, was pushing leader Acosta when the accident happened.

Acosta lost speed because of a technical issue and Marquez hit his bike, veering off the track into a terrible crash before being taken to hospital, conscious.

Last weekend, Alex Marquez's older brother Marc, the reigning champion, was injured after another violent crash at Le Mans.

The second major incident was a collision involving Zarco, Luca Marini and Francesco Bagnaia.

Zarco was taken by ambulance to hospital for checks after he was caught up with Bagnaia's bike.

LCR MotoGP team boss Lucio Cecchinello said Zarco had pain in "the femur area", his left leg and knee.

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