Mercedes driver Valtteri Bottas topped the first morning of 2020 Formula 1 pre-season testing at Barcelona, which ran without red flag disruption throughout.
On a sunny day at Barcelona, Bottas - who will hand over the W11 to Lewis Hamilton for the afternoon session - set a best time of 1m17.313s on the C3 Pirelli tyre, the middle compound in the manufacturer's range for testing, as he completed 79 laps.
Bottas initially put Mercedes at the top of the times shortly after Williams driver George Russell led the field out of the pits at 9am local time.
But the Finn's 1m29.375s on the C2 tyres did not last long, as Carlos Sainz Jr soon took over for McLaren with a 1m19.873s.
Sainz spent most of the opening hour slowly lowering the benchmark time on the C3 tyres, before going quicker again shortly after one hour had been completed on the C2s.
Sergio Perez then grabbed first place for Racing Point with a 1m18.037s, also set on the C2 tyres.
Bottas and Perez exchanged the top spot as they both ran the C3 rubber after that, before Bottas put in the morning's best time around 15 minutes before start of the final hour.
Perez ended up 0.062 seconds adrift, as Red Bull's Max Verstappen, who completed the most laps of any driver on the first morning with 91, completed the top three.
Sainz finished the morning in fourth place, just ahead of Renault's Esteban Ocon.
Russell spent the early running going out and then taking to the pitlane, so one hour and 45 minutes had passed before he set a lap time.
But the British driver worked his way up the order thereafter to end the morning in sixth place on a 1m18.168s.
Charles Leclerc took over driving duties for Ferrari before the action getting underway, as Sebastian Vettel - who had been scheduled to drive - felt unwell and the Scuderia opted to make a change.
Leclerc set the seventh-fastest time, a 1m18.289s, and completed 64 laps. Robert Kubica finished eighth for Alfa Romeo after completing his half-day of running for the team in the first test as part of his role as the squad's reserve driver.
His best lap of 1m18.386s was 1.073s adrift of Bottas's best, and Kubica will hand over the C39 to Antonio Giovinazzi for Wednesday afternoon's running.
Kevin Magnussen was ninth for Haas, with Daniil Kvyat rounding out the field for AlphaTauri.
Kvyat's best time was 1.171s slower than Bottas's, which reduced the gap covering the whole field in the session's final moments significantly.
The Russian driver looked set to go even faster with his final lap, but he aborted the run at the last moment.
Wednesday morning times
|2||Sergio Perez||Racing Point/Mercedes||1m17.375ss||0.062s||58|
|3||Max Verstappen||Red Bull/Honda||1m17.787ss||0.474s||91|
|4||Carlos Sainz Jr.||McLaren/Renault||1m18.001ss||0.688s||64|
|8||Robert Kubica||Alfa Romeo/Ferrari||1m18.386ss||1.073s||57|