Marquez to the top now and into the 1:29s. 0.189s ahead of Acosta now on a 9-lap-old medium rear tyre, which suggests this is about Sprint preparation.
A few riders back out on track now, still race running. Luca Marini currently tailing Marc Marquez who is about to push the pace on a little.
A lot of riders back in pit lane now having done around 13 minutes of race preparation.
46 minutes remaining, as VR46's Franco Morbidelli pops up to fifth.
Pedro Acosta to the top now, 0.005s ahead of Marquez. Race runs going on at the moment, and there's half-a-tenth covering the top four.
Jack Miller has gone down at the final corner, it looks like. He's up and okay.
Mir currently tailing Bagnaia and ahead of him on the timesheets, which is perhaps quite encouraging for Honda. Mir currently third, Bagniaa fourth.
Marc Marquez to the top now ahead of Joan Mir and Alex Marquez.
Early pace here in Practice set by Johann Zarco on a 1:30.484. Bagnaia's lap record from Q2 last year is a 1:28.700, for reference.
Pit lane is open now in Buriram and the MotoGP riders are heading out for one hour of Practice.
It was not such a stellar morning for Francesco Bagnaia in FP1, he finished 10th and over 0.7s behind his new teammate, but he was using the soft front tyre compared to Marquez's hard front.
Other notable performances this morning included Jack Miller in fourth place, and perhaps most surprising was Ai Ogura in sixth, less than 0.5s behind Marquez.
Marc Marquez, who was fastest on both days of the preseason test at Buriram, was fastest in this morning's MotoGP FP1 session by 0.158s from Franco Morbidelli, while Fabio Quartararo was 0.342s back in third place.
Welcome back to live coverage of today's MotoGP practice sessions from Buriram. Afternoon practice has just concluded for this year's fairly unattractive Moto2 field with Diogo Moreira fastest from Manuel Gonzalez.
For MotoGP, Practice will be underway in just over 10 minutes.
The chequered flag is waving and Marc Marquez finishes opening practice on top of the timesheets ahead of Franco Morbidelli, Fabio Quartararo and Jack Miller.
A red Ducati runs wide... you've guessed it, Bagnaia again.
Rookie Ai Ogura impresses by climbing to sixth place in the final minutes.
The live tyre data says Quartararo was on a new soft rear, but again the tyre info doesn't seem too reliable this morning (the TV graphics say he's on hard front and rear!)
Franco Morbidelli and Fabio Quartararo now squeeze between Marc Marquez and Miller.
Jack Miller rockets to 2nd place for Pramac Yamaha!
Bagnaia puts a lap together and rises to 5th place, but 0.7s from team-mate Marquez.
We probably won't know for sure who is using what tyres until the official results are issued.
Meanwhile Bagnaia runs off yet again.
Both Marc Marquez and Bagnaia are now listed on hard tyres front and rear according to the graphics. But the timing info says they are using the medium rear.
Replays show Acosta getting his RC16 sideways under braking, much more than Marquez and Bagnaia.