Maverick Vinales and Alex Marquez traded the fastest time in the opening quarter of the session, the Gresini rider setting the early pace on a 1m32.030s before Vinales moved the goalposts with a time of 1m31.657s.
Marquez struck back with a 1m31.486s just after the 15 minute mark, before Vinales went 0.002s quicker to snatch the top spot again.
The 28-year-old’s time of 1m31.484s remained unbeaten until the final 10 minutes of the session, when his Aprilia team-mate Espargaro improved to a 1m31.171s to lead the field by three tenths of a second.
However, Aprilia wouldn’t end the session on top, after Martin broke the 1m31s barrier with just five minutes left on the clock to steal the timelight for Pramac
Martin’s lap of 1m30.520s put him 0.238s at the front, after Vinales made a late improvement to 1m30.758s in an unsuccessful bid to reclaim the top spot.
Pol Espargaro jumped to third with an impressive 1m31.012s effort on his Tech3 KTM, leaving his brother Aleix fourth in the final order.
Fifth place went to Franco Morbidelli on the fastest of the two Yamahas, while Augusto Fernandez backed up the pace of his more experienced team-mate Espargaro with a solid sixth-place finish.
Fabio di Giannantonio, who has been linked with a move to Repsol Honda in 2024, was seventh for Gresini with a time identical to RNF Aprilia rider Raul Fernandez.
Di Giannantonio’s team-mate Marquez failed to improve on his early-session flier and slipped to ninth in the final order, 0.966s in arrears of Martin.
The top 10 was completed by Bagnaia, who arrived in Thailand 29 points ahead of his chief championship rival Martin.
Despite finding some more time in the final five minutes of practice, Bagnaia was only the fourth-quickest Ducati in the session as he ended up 0.987s down on Martin with a best effort of 1m31.507s.
He was followed by LCR’s Takaaki Nakagami on the top Honda and the second Yamaha of 2021 champion Fabio Quartararo.
The factory KTM team had a low key session as both Jack Miller and Brad Binder finished over a second down in 13th and 14th respectively, while VR46 duo Luca Marini and Marco Bezzecchi were also off the pace in 15th and 16th places.
Marc Marquez was a distant 18th on the factory Honda, two places ahead of team-mate Joan Mir.
No crashes were recorded during 15 minutes of practice, although a number of rider had small moments exiting corners.
MotoGP Thailand GP – FP1 results: