Valtteri Bottas led a Mercedes 1-2 in FP1 for the Spanish Grand Prix but the session did little to shed light on the tyre-wear that could define the race on Sunday.
Bottas has half a tenth ahead of Lewis Hamilton while Max Verstappen was third, nearly a full second behind the Finn.
Alex Albon had to return to the pits at one stage with the team suspecting a problem with the car but was able to return to the track later in the session and placed ninth.
Charles Leclerc continued his good form at the top of the midfield a quarter of a second behind Verstappen after recording a third and fourth across the two weeks at Silverstone.
His teammate Sebastian Vettel had a welcome return to form to place fifth, Vettel’s running with a new chassis after the team said they found cracks on the one he’d been running previously.
Another surprise performer was Romain Grosjean who was sixth and followed on from a decent last weekend when he reached Q2 and started 13th.
Haas have sometimes over-performed in practice sessions this season but it marks a positive step for both the team and driver, as Grosjean was ahead of most midfield teams.
Kevin Magnussen was ninth in the other Haas and only 0.015s behind Albon.
Sergio Perez split the bunch on his return to racing after two weeks out with a positive coronavirus test.
After his replacement Nico Hulkenberg impressed at Silverstone, the pressure is on for Perez to match those results and he seems to be back on the pace, although still a way behind the third-place Hulkenberg took in qualifying last weekend.
The other Racing Point of Lance Stroll rounded out the top ten, ahead of a trio of Esteban Ocon and the two McLarens who were separated by just 0.011 seconds.
Daniel Ricciardo had a tough session down in 18th place despite completing 31 laps, and requested a front-wing change after an hour.
Roy Nissany, number 40, sat in the session for George Russell, the second time the Brit has missed a session after Jack Aitken took FP1 at the Styrian Grand Prix.
Nissany, who’s 18th in Formula 2 this year with one point, brought up the rear having driven 25 laps and sitting three-tenths behind Nicholas Latifi.