Petronas SRT rider Fabio Quartararo topped the first day of 2020 MotoGP pre-season testing in Malaysia, while his factory Yamaha counterpart Maverick Vinales crashed.
Last season's top rookie Quartararo was the first out on track at Sepang on Friday morning, though it was Aprilia's Aleix Espargaro who set the initial pace in the opening hour.
Espargaro, who took part in the shakedown earlier in the week, guided his radically redesigned RS-GP to a time of 1m59.427s to dip underneath the existing race lap record.
The outright lap record of 1m58.303s belongs to Quartararo, who posted that on his way to pole for last year's Malaysian Grand Prix.
After two hours, the SRT rider put his 2019-spec M1 top of the pile with a 1m58.945s, which would ultimately go unchallenged.
Quartararo will ride the full 2020-spec M1 on Saturday, but will have just one of those at his disposal.
The morning running was briefly halted by a red flag for an incident involving one of the Yamaha test riders, though a greater lull would follow later in the day as a burst of rain kept the track quiet for some time.
Another shower late on brought running the day to a premature end with just under 10 minutes to go.
The Pramac Ducati pairing of Francesco Bagnaia and Jack Miller signalled the resumption of running with just under two hours to go, though Quartararo's benchmark remained intact.
Quartararo's team-mate Franco Morbidelli trailed him heading into the lunch break by 0.051 seconds, and held onto second place come the chequered flag.
Morbidelli will not have machine parity with Quartararo or the works team Yamaha riders anymore this year, and is instead riding the 'A-spec' M1 - essentially, the bike the factory Yamaha riders finished last November's tests with.
Alex Rins led the Suzuki charge in third spot as he worked through his programme on the new-spec GSX-RR, while LCR's Cal Crutchlow was top Honda rider in fourth ahead of Miller.
Vinales ended the day sixth spot, having crashed earlier in the day at the Turn 11 right-hander.
He, along with team-mate Valentino Rossi - who was 10th fastest - had three M1s at his disposal: two 2020-spec machines, and the 'A-spec' bike from November.
Early pacesetter Espargaro was seventh ahead of his KTM-mounted brother Pol, who also took part in the shakedown earlier this week.
Joan Mir was ninth on the sister Suzuki, with Rossi rounding out the top 10 ahead of the first of the works team Ducatis of Andrea Dovizioso.
Reigning world champion Marc Marquez shadowed Dovizioso, as he marks his first MotoGP outing since undergoing surgery on a right shoulder injury in the winter.
Admitting ahead of the test he'd only be at "70%" strength, Marquez only completed 37 laps and managed a best time of 1m59.675s.
His brother and new team-mate Alex was just a further 0.021s adrift in 13th, while Johann Zarco was 1.5s off the pace in 19th on his first outing on the Avintia Ducati GP19.
Sepang day one times
|1||Fabio Quartararo||Petronas Yamaha||Yamaha||1m58.945s||52|
|2||Franco Morbidelli||Petronas Yamaha||Yamaha||0.051s||62|
|4||Cal Crutchlow||LCR Honda||Honda||0.289s||39|
|5||Jack Miller||Pramac Ducati||Ducati||0.291s||47|
|17||Francesco Bagnaia||Pramac Ducati||Ducati||1.191s||53|
|19||Johann Zarco||Avintia Ducati||Ducati||1.519s||54|
|22||Tito Rabat||Avintia Ducati||Ducati||1.805s||54|
|23||Takaaki Nakagami||LCR Honda||Honda||1.870s||31|
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