Valtteri Bottas topped opening practice for the Spanish Grand Prix with Mercedes' Finnish driver ending Friday's morning session 0.033sec quicker than the Red Bull of Max Verstappen.
Championship leader Lewis Hamilton was on the tails of the front two with the Briton who is targeting his 100th pole this weekend 0.123s off his Mercedes teammate.
Lando Norris's bright start to the season continued for McLaren with the fourth quickest time at the Montmelo circuit ahead of the two Ferraris of Charles Leclerc and Carlos Sainz.
Two drivers spun off: Haas' Russian rookie Nikita Mazepin on his first flying lap, and Robert Kubica, Aston Martin's reserve driver, midway through the session prompting a red flag interuuption as his car was retrieved from the gravel.
Hamilton leads the drivers standings by eight points from Verstappen ahead of this fourth round of the championship.
The cars will be back out on the track for second practice starting at 1300GMT.
Spanish Grand Prix first practice times
Valtteri Bottas (FIN/Mercedes) 1min 18.504sec (25 laps), Max Verstappen (NED/Red Bull-Honda) 1:18.537 (19), Lewis Hamilton (GBR/Mercedes) 1:18.627 (22), Lando Norris (GBR/McLaren-Mercedes) 1:18.944 (24), Charles Leclerc (MON/Ferrari) 1:18.996 (25), Carlos Sainz Jr (ESP/Ferrari) 1:19.020 (22), Pierre Gasly (FRA/AlphaTauri-Honda) 1:19.062 (26), Sebastian Vettel (GER/Aston Martin-Mercedes) 1:19.234 (24), Sergio Pérez (MEX/Red Bull-Honda) 1:19.349 (17), Lance Stroll (CAN/Aston Martin-Mercedes) 1:19.429 (25), Yuki Tsunoda (JPN/AlphaTauri-Honda) 1:19.669 (22), Esteban Ocon (FRA/Alpine-Renault) 1:19.681 (25), Antonio Giovinazzi (ITA/Alfa Romeo-Ferrari) 1:19.694 (23), Daniel Ricciardo (AUS/McLaren-Mercedes) 1:19.732 (24), Fernando Alonso (ESP/Alpine-Renault) 1:19.950 (25), Nicholas Latifi (CAN/Williams-Mercedes) 1:20.270 (25), Roy Nissany (ISR/Williams-Mercedes) 1:20.700 (23), Mick Schumacher (GER/Haas-Ferrari) 1:20.766 (23), Robert Kubica (POL/Alfa Romeo-Ferrari) 1:21.887 (13), Nikita Mazepin (RUS/Haas-Ferrari) 1:21.976 (22)