Carlos Senz led Charles Lecler in a Ferrari One-Two in his first practice at the Australian Grand Prix.
Sainz was 0.571 seconds ahead of his teammate, whose effort on a new set of soft tires was affected by an off-track moment when he came out of the hole.
Red Bull’s Sergio Perez and Max Verstappen are third and fourth, with Perez slowing down 0.59 seconds.
Mercedes’ Lewis Hamilton was seventh, behind McLaren’s Lando Norris and Alpine’s Esteban O’Connor, 1.2 seconds slower.
Melbourne’s Albert Park track has been modified to allow F1’s return to Australia after a two-year absence due to the epidemic.
A chicken has been removed and re-profiled in an attempt to make racing at some corners more exciting in a circuit famous for the difficulty of overtaking.
No major incidents occurred during the session, although several drivers fled the road.
Leclerc moved to the third-last corner towards the end of the session while pressing hard tires in addition to his off after starting practice.
Kevin Magnussen smiled and ran wide in turn three, misunderstanding his braking.
And Sebastian Vettel, after missing the first two races of the season with Covid, came back for Aston Martin and lost strength and stopped on the track in a cloud of smoke.
Behind Hamilton, McLaren’s Daniel Ricciardo, Alpine’s Fernando Alonso and Alfa Romeo’s Valteri Botas have completed the top 10.
Alonso’s Alpine has been fitted with a new engine for this weekend – the third of its season when only three have been approved for the full championship.
Alpine discovered a problem with Alonso’s engine after the first race in Bahrain and made a new fit for the second race in Saudi Arabia. It suffered a water-pump failure that caused irreparable damage to the internal combustion engine.
Alonso’s problems mean he will inevitably face grid fines at the end of the year for using more than the permitted number of power-unit components.
The second session starts at 07:00 BST.