Fabio Quartararo set the fastest-ever MotoGP lap of the Sepang circuit with a 1m59.027s in FP1 for the Malaysian Grand Prix to lead a Petronas SRT 1-2.
The Frenchman won out of an SRT Yamaha shootout in the closing stages of the 45-minute session, pipping team-mate Franco Morbidelli by 0.083s to head a 1-2 to kick off the team's home race.
The tiny margin was enough to leave Quartararo on the right side of the lap record, his 1m59.027s a new official benchmark at the Sepang circuit.
Quartararo's final lap was a fine response to his team-mate, who had knocked him off top spot moments earlier with a 1m59.110s.
Maverick Vinales was third best of a flourish of late improvements, making it a Yamaha top three with a 1m59.218s on his final lap on the works team M1.
The Spaniard led the way for the majority of the session, going quickest early with a 2m00.373s, before dipping under the two-minute barrier with a 1m59.955s at the 20-minute mark.
It wasn't until the late rush that his time was overhauled.
Marc Marquez finished up fourth quickest, the reigning world champion provided the majority of the highlights from a straightforward session.
It started with a low-side near-miss at Turn 2 on his opening run, before his Honda rolled to a stop 12 minutes in, the recovery involving a detour through the back of the paddock.
He was swiftly back in action, his 1m59.517s coming on his final run.
Andrea Dovizioso on the Ducati and Suzuki's Alex Rins were next, followed by Aleix Espargaro (Aprilia), Valentino Rossi (Yamaha), LCR's Cal Crutchlow and Jack Miller on the Pramac GP19.
It was another tough session for Jorge Lorenzo, who ended up way down in 18th, 2.4s off the pace and two spots behind LCR stand-in Johann Zarco.
Tech3 rider Miguel Oliveira's ongoing participation has been left in serious doubt after FP1, the wrist injuries from his Phillip Island crash flaring up during the session.
He only completed four laps, the best of which was more than 6s off the pace, and exited the Tech 3 garage with more than a quarter of an hour to go.
Avintia's Tito Rabat will take no part in this weekend's Malaysian GP due to an ongoing hand injury, and will not be replaced after the team's plans to run former Moto3 racer Eric Granado fell through.
|1||Fabio Quartararo||Petronas Yamaha||Yamaha||1m59.027s||-||18|
|2||Franco Morbidelli||Petronas Yamaha||Yamaha||1m59.110s||0.083s||16|
|9||Cal Crutchlow||LCR Honda||Honda||1m59.975s||0.948s||16|
|10||Jack Miller||Pramac Ducati||Ducati||1m59.996s||0.969s||14|
|13||Karel Abraham||Avintia Ducati||Ducati||2m00.874s||1.847s||15|
|15||Francesco Bagnaia||Pramac Ducati||Ducati||2m01.000s||1.973s||16|
|16||Johann Zarco||LCR Honda||Honda||2m01.038s||2.011s||16|
|19||Hafizh Syahrin||Tech3 KTM||KTM||2m01.579s||2.552s||14|
|21||Miguel Oliveira||Tech3 KTM||KTM||2m05.412s||6.385s||4|