Ferrari driver Charles Leclerc led the early running as pre-season testing continued at the Bahrain International Circuit on Thursday.
After completing the most mileage of any team and featuring towards the top of the timesheets during the first test week in Barcelona, the Italian team displayed further early promise with their F1-75.
Leclerc clocked several laps fast enough for P1, improving to a time of 1:34.531 shortly before the two-hour mark, having gone purple in all three sectors with the yellow-marked Medium C3 tyre compound.
Mercedes were next up, having made the early headlines with a 'sidepod-less' version of their W13, which caused a stir up and down the paddock.
Lewis Hamilton's time was some two seconds down on Leclerc, using the same C3 rubber, as drivers and teams gradually got up to speed in the vastly different testing conditions to Barcelona.
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Mileage the priority for drivers and teams early on
Hamilton was one of three drivers, along with Red Bull's Sergio Perez and Alfa Romeo rookie Guanyu Zhou, to hit the 30-lap milestone during the first two hours of testing action.
Perez placed third on the Hard C2 compound, which was also used by Aston Martin's Sebastian Vettel en route to fourth, while McLaren's Lando Norris - stepping in for the unwell Daniel Ricciardo - completed the top five on the Soft (C4) rubber.
While most teams got some solid early running under their belts, Norris was the only driver who did not reach double lap figures by the halfway point of the morning session, with no explanation from McLaren.
At Williams, F1 returnee Alex Albon suffered with a heating problem in the FW44, resulting in a literal hot seat that required checks back in the garage.
Haas were unable to take part in the morning session, after freight delays, while there were no other incidents of note, aside from the occasional lock-up and off-track excursion.
You can stay up to date with all the action from Bahrain in the dedicated RacingNews365.com live blog.
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