The best time was around a second slower than Bottas achieved during pre-season testing, which came in more favourable track conditions, and on the C5 compound – which is unavailable this weekend.
Bottas used the Soft tyres – which for this weekend is the C3 compound – to finish 0.039s clear of Mercedes team-mate Lewis Hamilton.
Mercedes miles in front
As has been the case in qualifying trim this year Mercedes was significantly clear of its nearest opponent, with last weekend’s victor Max Verstappen best of the rest for Red Bull.
Verstappen’s best time was 0.939s down on Bottas’ benchmark and he was the only driver to finish within a second of the Mercedes drivers.
Ferrari displayed relatively stronger speed as Charles Leclerc and Sebastian Vettel, running a new chassis, classified fourth and fifth, separated by just 0.011s.
Customer team Haas also put in a more competitive showing at historically one of its stronger circuits, with Romain Grosjean sixth and Kevin Magnussen ninth.
Perez returns to action
After missing two events, and spending seven days in self-isolation in a Milton Keynes apartment, Racing Point’s Sergio Perez returned to Formula 1 action.
Perez, whose RP20 was driven by Nico Hulkenberg in his absence, was cleared to re-enter the paddock after returning a negative coronavirus test earlier in the week.
Perez was the quickest of the Medium tyre runners as he classified seventh overall, in front of Red Bull’s Alexander Albon, Magnussen, and Racing Point team-mate Lance Stroll.
McLaren finished 11th and 13th, with local representative Carlos Sainz Jr. ahead of Lando Norris, split by the quickest Renault of Esteban Ocon.
AlphaTauri and Alfa Romeo were next up, with Pierre Gasly, Antonio Giovinazzi and Kimi Raikkonen covered by less than a tenth of a second, and Daniil Kvyat – running a fresh Honda engine – close behind.
Renault’s Daniel Ricciardo and Williams’ Nicholas Latifi were the slowest of the regular runners
A new face at Williams
Williams handed George Russell’s FW43 to Formula 2 racer and test driver Roy Nissany for the 90-minute session.
Nissany, son of one-time Minardi tester Chanoch, joined Williams for 2020 with backing from his native Israel.
He finished at the foot of the timesheets, via a spin under braking for Turn 10, but was only three-tenths down on regular driver Latifi.
Russell will return to action for the second session.
Second practice for Formula 1’s Spanish Grand Prix will begin at 15:00 local time.