Marc Marquez is under investigation for tyre pressure.
It's Sprint victory for the 11th time from 12 races this year.
Acosta second from Bastianini, who holds on from Bezzecchi.
Fourth for the Aprilia rider, while Quartararo rounds out the top-five.
Raul Fernandez passed Bagnaia on the last lap for sixth, so Bagnaia ends up P7.
Zarco and Espargaro take the final points.
Binder rounds out the top-10 ahead of Martin.
Marquez now leads again after passing Acosta in the stadium section.
Acosta second now from Bastianini, but he's under pressure from Bezzecchi.
2 to go now and it's still Acosta from Marquez and Bastianini.
Bagnaia's done, he's 6th and nowhere near Bezzecchi, he's more worried with Fernandez now.
Bezzecchi up to fourth, past Quartararo, at turn one of lap 9.
Acosta leads Marquez and Bastianini.
Quartararo P4 and now Bezzecchi 5th after he passed Bagnaia.
Now Bagnaia's dropped the positions, he can't turn. He's basically in the same position as he's been in in previous Sprints this year where he falls behind riders and then can't pass. This time it's been forced on him, seemingly, by tyre pressure warnings.
Now Marquez has slowed up to allow Acosta by. He was 3s clear. This is tyre pressure issues for the Ducati riders.
5 laps to go.
Crash for Di Giannantonio - he was 18th. He's now riding back on a scooter.
Strange lap for Bagnaia. He let Acosta through on the run to turn five, and then was passed by Bastianini and Quartararo, but he's now picked the pace up again. Totally bizarre.
Marquez now 1s clear of Bagnaia as he sets the fastest lap of the race at 1:53.243.
Acosta was pressuring Bagnaia for second one-and-a-half laps ago but he's now slipped back to Quartararo and Bastianini.
Half-a-second now for Marquez, who has the same gap back to Acosta. Then it's Bastianini, Quartararo, Fernandez, Bezzecchi, Martin, Zarco, and Pol Espargaro in the top-10.
Quartararo ran slightly wide at turn 10 on the last lap and Bezzecchi tried to take advantage. But Quartararo closed the door, fairly, and Bez had to sit up to avoid. He's back to P7 now behind Raul Fernandez.
Bastianini having his best ride on a KTM - P5 and pressuring Quartararo for fourth.
Augusto Fernandez and Nakagami both down at turn three. Fernandez lost the rear while on the inside of Nakagami and took them both out. Nakagami looked hurt in the gravel, Fernandez went to check on him.
Acosta up to third at turn one beginning lap two, Quartararo touched the grass exiting the final corner.
Marquez leads lap one from Bagnaia and Quartararo, Bagnaia seeming more comfortable than usual in Sprints.
Bad starts for Alex Marquez from 8th, he's 19th after spinning off the start, and Mir who is 22nd and last from P5 on the grid after he ran on at turn three.
Marquez leads at turn three, passes Bagnaia on the inside.
It's lights out in Brno for the Sprint, and a holeshot for Bagnaia ahead of Marquez and Quartararo.
Riders are off on their warm-up lap for the Czech Sprint.
Paolo Bonora, Aprilia Racing Team Manager, just telling the international TV feed that they're still "evaluating" the medium rear for the Sprint due to the warmer temperatures this afternoon. 24C air temperature, 37C track temperature.
Some split on tyre choice at the moment.
Everyone on medium-compound front tyre.
At the rear, though, some differences in opinion.
Bezzecchi, Mir, Zarco, Martin, Marini, Nakagami, Ogura, Fernandez all with the soft-compound rear.
Everyone else on the medium rear.
It has been a curious weekend for Aprilia. Both factory riders in Q2 from the wet Practice on Friday, joined by Raul Fernandez in Q2 after the Trackhouse rider finished second to Bagnaia in Q1.
Of course, the factory team has Jorge Martin back this weekend - he starts 12th this afternoon and has generally been quite solid this weekend so far. He will be looking for his first points for the Noale factory today but, of course, the primary objective at this point for the Spaniard is getting through the weekend and into the summer break healthy.
Marco Bezzecchi has also been good this weekend and qualified fourth, but he's also crashed three times, including in Q2. He's chasing a third straight Sprint podium today.
It was a difficult qualifying for Alex Marquez, his worst of the year, in fact, down in P8. He comes into this race 83 points behind his brother, Marc, in the riders' standings.
He's been increasingly clear recently that his main target for 2025 now is maintaining second place in the standings from Bagnaia, who is 62 points behind the Gresini rider.
From eighth, he will have work to do this afternoon to prevent that gap to Bagnaia from decreasing ahead of tomorrow's Czech Grand Prix.
There was some concern at the end of qualifying that a penalty could have been coming the way of Marc Marquez after he crashed at the penultimate corner while Johann Zarco and his LCR Honda were already in the gravel.
But the Spaniard crashed at turn 13 having already entered the yellow flag zone before the yellows were thrown for the Zarco crash. So, no penalty for the factory Ducati rider.
Marquez said afterwards that he had been distracted, that being the cause of his crash that probably cost him pole position.
20 minutes until the Sprint gets underway and the riders are off on their sighting lap ahead of the Sprint.
Francesco Bagnaia is on pole for the first time this year today.
He'll start alongside Marc Marquez and Fabio Quartararo on the front row.