Carlos Sainz and Ferrari set the pace as the second morning of pre-season testing got underway at the Circuit de Barcelona-Catalunya.
On another sunny, pleasant day at the Spanish Grand Prix venue, Sainz initially moved to the front with a time of 1:21.010 on the Medium (C3) tyre, before improving to a 1:20.890 on the same compound.
It compares to the 1:20.165 posted by teammate Charles Leclerc on the C3 rubber on Wednesday, and the 1:19.568 from McLaren driver Lando Norris, who made use of the more aggressive Soft C4s.
AlphaTauri's Pierre Gasly and Williams driver Alex Albon also posted their best times on the C3s, as they slotted into second and third respectively.
The top three all comfortably worked their way towards a race distance, with Sainz leading the individual lap charts by getting 34 laps under his belt.
Hamilton and Red Bull quiet, more problems for Alfa Romeo
Further down the order, it was a less productive morning for Mercedes driver Lewis Hamilton and Red Bull.
Hamilton spent most of the early hours towards the bottom of the times, with only a handful of laps to his name, though rose to fifth position shortly before the two-hour mark with a run on Hard tyres.
After Max Verstappen's solo drive to 147 laps on Wednesday, Sergio Perez completed fewer than 20 over his first two hours of scheduled track time in the Red Bull, initially appearing with aero rakes on his car and not stringing runs together at the same cadence as his teammate.
But the situation was worse at Alfa Romeo, with Valtteri Bottas struggling to hit double figures in terms of laps. It comes after an opening day that was plagued by delays, including an early issue with the C42's floor.
Meanwhile, Daniel Ricciardo and Esteban Ocon made their first appearances of the pre-season for McLaren and Alpine respectively.
You can stay up to date with all the action from Barcelona in the dedicated RacingNews365.com live blog.
With F1 pre-season testing getting underway in Barcelona this week, our journalists Dieter Rencken, Mike Seymour and Thomas Maher look ahead to what to expect.