Reigning MotoGP champion Marc Marquez set the pace in the opening premier-class session of the Czech Grand Prix weekend at Brno.

Marquez backed up his Hungarian Grand Prix-dominating form with a superb start out of the blocks here, leading the vast majority of the 45-minute session.

Despite not changing his front or rear tyre, he looked on course to lower his 1m53.303s benchmark further in the end when he crashed going through the Turn 7 left-hander.

But he stayed top of the timing screens, ending the session two tenths clear of his nearest rival - Yamaha's Fabio Quartararo.

Quartararo's position in the order was flattered by the use of fresh medium tyres, front and rear, though still represented a considerable step forward relative to his form at Mugello and Balaton Park.

Raul Fernandez, who ran a fresh front tyre and used rear in the end of the session, was third-fastest and best of the Aprilias - despite coming into the weekend with fitness complications, having missed media day on Thursday due to appendix inflammation.

Honda rider Joan Mir (fresh tyres front and rear in the end) and Fernandez's Trackhouse team-mate Ai Ogura (fresh front, used rear in the end) propped up the top five, while Pecco Bagnaia in sixth was next-best of those behind Marquez, who stuck with the same set through the session.

Three riders - Pedro Acosta, Maverick Vinales and Diogo Moreira - crashed in the early minutes of the session, all three rejoining the action fairly swiftly.

Alex Marquez, who returned to MotoGP action in this session after an injury absence forced by his heavy Barcleona crash, was 1.2s off the pace in 18th.

He, like Fernandez, is due to be medically reviewed after FP1 to confirm participation in the rest of the weekend.

Session results

1 Marc Marquez (Ducati) 1m53.303s
2 Fabio Quartararo (Yamaha) +0.200s
3 Raul Fernandez (Trackhouse Aprilia) +0.210s
4 Joan Mir (Honda) +0.220s
5 Ai Ogura (Trackhouse Aprilia) +0.318s
6 Pecco Bagnaia (Ducati) +0.376s
7 Fermin Aldeguer (Gresinbi Ducati) +0.476s
8 Fabio Di Giannantonio (VR46 Ducati) +0.484s
9 Pedro Acosta (KTM) +0.518s
10 Luca Marini (Honda) +0.542s
11 Toprak Razgatlioglu (Pramac Yamaha) +0.623s
12 Alex Rins (Yamaha) +0.625s
13 Maverick Vinales (Tech3 KTM) +0.672s
14 Jorge Martin (Aprilia) +0.712s
15 Franco Morbidelli (VR46 Ducati) +0.872s
16 Marco Bezzecchi (Aprilia) +0.891s
17 Brad Binder (KTM) +0.946s
18 Alex Marquez (Gresini Ducati) +1.216s
19 Diogo Moreira (LCR Honda) +1.385s
20 Jack Miller (Pramac Yamaha) +1.487s
21 Enea Bastianini (Tech3 KTM) +1.591s
22 Cal Crutchlow (LCR Honda) +2.003s