LCR Honda's Cal Crutchlow ended the opening day of running from the Chang International Circuit fastest of all, as the second pre-season MotoGP test gets underway in Thailand.
In preparation for the series' first race in Thailand in October, MotoGP will spend three days in Buriram in order to gather information for the event later this year, while the riders also carry on with the development of their '18 machines.
Honda's Marc Marquez was the early session leader with a 1:32.333s, before raising that benchmark to a 1:30.912s.
The Spaniard remained top of the pile for much of the day, before Honda stablemate Crutchlow edged ahead with a 1:30.797s despite a tumble at the final corner.
The Briton, who spent much of the day evaluating parts for the factory, remained on top of the timesheets as the chequered flag fell, though did come under threat in the closing stages from Suzuki's Alex Rins.
Rins, who along with team-mate Andrea Iannone, had a new exhaust to try on Friday, with the Spaniard missing out of the headline time by just 0.012s. Marquez completed the top three.
Andrea Dovizioso was fourth fastest as Ducati debuted its new aerodynamic fairing. The Bologna factory reportedly has three versions of the package, with both Dovizioso and Sepang pacesetter Jorge Lorenzo trialing a 'short' and 'long' design – the latter bearing a resemblance to the fairing used last year.
Dani Pedrosa completed the top five on the sister factory Honda, the Spaniard joining Crutchlow in sliding off at the tricky Turn 12.
Pramac pairing Danilo Petrucci and Jack Miller followed Pedrosa on the timesheets, with Valentino Rossi – who turns 39 today – top Yamaha runner as the Japanese marque focused its efforts on race set-up.
Iannone and Lorenzo rounded out the top 10, with Maverick Vinales a few thousandths adrift in 11th ahead of Tech3's Johann Zarco, who has reverted back to the '16 M1 frame for the remainder of testing.
Tito Rabat was just 0.7s from top spot on the Avintia Ducati despite a crash at Turn 7, with fellow GP17 runner Alvaro Bautista close behind in 14th – the Angel Nieto rider added his name to the list of fallers at the final turn along with Xavier Simeon on the second Avintia bike.
Aleix Espargaro rounded out the top 15 ahead of Aprilia team-mate Scott Redding, who endured numerous mechanical issues, including an engine failure on his sole '18 RS-GP. LCR's Takaaki Nakagami was top rookie in 17th.
Hafizh Syahrin, who has been called up to test the second Tech3 Yamaha as rumours mount that the Malaysian will replace Jonas Folger this season, was 24th on his MotoGP debut and a respectable 2.3s off the pace.
