Valentino Rossi topped a tight opening free practice for the Qatar MotoGP Grand Prix, with new Honda recruit Jorge Lorenzo shadowing him by 0.079 seconds.
Reigning world champion Marc Marquez led for much of the session on his works Honda, before Rossi guided the new-look Monster Yamaha to the top of the pile with a 1:55.048s at session's death.
LCR's Cal Crutchlow posted the initial benchmark at 1:57.648s in the opening moments of FP1, before new works Ducati rider Danilo Petrucci went nine tenths clear shortly after.
Honda returned to the top the standings, with Marquez leaping to first with a 1:55.667s, before improving by two tenths on his follow-up tour.
A further improvement to 1:55.164s put him within three tenths of the race lap record and put him just over tenth out of reach of Petrucci after 15 minutes of running.
The top two remained as so for much of the remainder of the session, while Marquez's Honda team-mate Lorenzo, Suzuki's Alex Rins and Rossi filled out the rest of the top five.
Changes started to come in the closing minutes, with Sepang Racing's Franco Morbidelli moving up to third just seconds after Rins had moved his GSX-RR into the top three.
Lorenzo finally deposed Marquez with a 1:55.127s with just over two minutes remaining, before former team-mate Rossi charged ahead by 0.079s.
Marquez held onto third, a further 0.037s adrift, with 2018 Qatar race winner Andrea Dovizioso fourth ahead of the sister factory GP19 of Petrucci.
Maverick Vinales made several attempts at taking top spot late on, but had to settle for sixth ahead of Yamaha stablemate Morbidelli and the leading Pramac bike of Jack Miller.
Rins was shuffled back to ninth at the chequered flag, while Takaaki Nakagami edged SRT's Fabio Quartararo out of the top 10 on his year-old LCR Honda.
Quartararo ended the first session as top rookie, with the Espargaro brothers of Pol [KTM] and Aleix [Aprilia] splitting him from fellow debutant Joan Mir on the Suzuki.
Early pacesetter Crutchlow faded to 17th as the dust settled, but was just eight tenths from top spot, while KTM duo Miguel Oliveira [Tech3] and Johann Zarco on the factory-run RC16 shadowing.
Oliveira's Tech3 team-mate Hafizh Syahrin was the first crasher of the 2019 season, the Malaysian coming off unscathed at the final corner at the start of the session.
