Honda's Marc Marquez topped the post-Catalan Grand Prix test on Monday by 0.104 seconds from Suzuki's Andrea Iannone.
All MotoGP teams bar the factory Ducati and its customer Nieto squads stayed behind at the Circuit de Barcelona-Catalunya for a day of testing to evaluate new parts, as well as a prototype 2019 front tyre from Michelin.
Tech3 Yamaha's Johann Zarco set the early pace, the Frenchman top of the timesheets at the end of the first hour with a 1:39.534s, while Avintia's Tito Rabat was just 0.072 seconds adrift in second.
After finishing a lowly seventh in Sunday's race, Zarco spent the day focusing fully on race simulations, completing a total of 72 laps.
Iannone, who was testing a new GSX-RR chassis, had replaced Zarco at the top of the standings by miday with a 1:39.020s, which stood as the benchmark through to the final few minutes of the session.
Rabat and Pramac's Danilo Petrucci – who concentrated on testing various new parts for Ducati – slotted in behind Iannone, though the latter's day ended early after a heavy crash at Turn 9.
Championship leader Marquez had a new Honda at his disposal, which was thought to have been a new chassis, and completed a total of 88 laps as he evaluated the new bike against his current spec ones.
The Spaniard was one of a handul of riders to return to track in the final hour for a few laps, and leaped up to second with a 1:39.230s. A 1:38.916s in the final three minutes put him top of the pile.
Iannone maintained second despite an eary finish, while Rabat completed the top three ahead of Petrucci and Zarco.
Cal Crutchlow was sixth on his LCR Honda as he tried small updates from HRC, with stablemate Dani Pedrosa seventh after a late lap of 1:39.736s on the second Repsol RC213V.
Alex Rins finsihed the day eighth on the sister Suzuki, with Maverick Vinales the leading factory Yamaha in ninth ahead of Pramac's Jack Miller, who worked on extracting the most from Michelin's soft tyres.
Valentino Rossi was a low-key 14th on the second factory M1, with Tech3 counterpart Hafizh Syahrin a tenth ahead in 13th, while Bradley Smith completed the top 15 as he tested a new aerodynamic fairing on his RC16.
The session was briefly red-flagged with an hour and 10 minutes remaining after Smith's team-mate Pol Espargaro crashed at the final corner. He was reported as unhurt.