Marc Marquez led Honda team-mate Jorge Lorenzo by 0.124 seconds in the opening practice ahead of the MotoGP Spanish Grand Prix at Jerez.
Marquez led the session after the opening few moments, and reclaimed top spot in the latter stages having been briefly deposed by Lorenzo to end the session fastest of all with a 1:37.921s.
The opening European session of the 2019 season was led in the early stages by Petronas SRT Yamaha rider Fabio Quartararo, who posted a 1:41.569s on the newly-resurfaced Jerez circuit.
The Moto2 graduate was soon deposed by Austin podium finisher Jack Miller on the Pramac Ducati by just under a tenth of a second, before 2018 Jerez race winner Marquez leaped to the head of the times with a 1:39.600s.
Marquez lowered the benchmark on his follow-up tour to a 1:38.450s to dip underneath the existing race lap record set by Honda team-mate Lorenzo, who shadowed him in second – albeit 0.7s adrift.
Championship leader Andrea Dovizioso slashed Marquez's advantage down to just over three tenths on his works Ducati, though Marquez would re-open his gap at just over mid distance with a 1:38.286s.
A flurry of fast laps in the closing moments was begun by SRT's Franco Morbidelli, who went second with a 1:38.478s to get to within a tenth and a half of Marquez
A 1:38.045 from Lorenzo moved him into the lead of the timesheets, while Marquez missed out by just 0.029s.
He would go fastest once more on his penultimate lap with a 1:37.946s, improving on his final tour to a 1:37.921s to open up a gap of 0.124s to end FP1 fastest of all.
Lorenzo held onto second, with Maverick Vinales securing third after a late 1:38.112s to end Friday morning as top Yamaha runner.
Jerez test pacesetter Takaaki Nakagami was fourth on his year-old LCR Honda, 0.020s clear of Dovizioso. Quartararo headed Miller, the second works Ducati of Danilo Petrucci, Morbidelli and Austin race winner Alex Rins [Suzuki].
KTM's Johann Zarco was an encouraging 12th and within a second of Marquez at the of FP1 despite a fast crash at the Alex Criville corner after the chequered flag had falled.
Zarco shadowed last year's Spanish GP pole man Cal Crutchlow [LCR], and led Suzuki's Joan Mir, Aprilia man Aleix Espargaro, and HRC wildcard Stefan Bradl.
Valentino Rossi – who trialled Yamaha's new Ducati-style swingarm wing – was a low-key 18th at the end of FP1, 1.4s off the pace. Aprilia wildcard Bradley Smith was 0.030s adrift in 19th as he gears up for his second race appearance on the RS-GP in 2019.
