Sainz was second fastest at the end of opening practice in his first official session for Williams behind early title-favourite Norris.

The ex-Ferrari pilot topped proceedings for much of the session, which was twice interrupted by red flags.

A crash for Oliver Bearman ripped the left-rear wheel free from his Haas as he spun to a halt exiting the Turn 10.

The Brit ran wide at the ultra-fast right-hander, bouncing through the gravel before he was pitched into a spin and, ultimately, the wall.

Bearman climbed out without injury or assistance as officials waved the red flag for the second time in the session.

Earlier, the red flag had been shown after Jack Doohan dropped a wheel over the back of the exit kerb at Turn 6.

Though the Alpine ace was able to continue unabated, thanks to the flattered kerbing for this year’s event, it dragged gravel onto the race track.

Officials took a conservative approach at the high-speed right-hander and halted running until it could be cleaned up.

When the track was clear, a lap midway through the session sent ripples up and down the pit lane when Sainz went fastest.

The Spaniard logged a 1:17.401s to edge ahead of Charles Leclerc, Oscar Piastri, and Max Verstappen at the time.

Sainz’s effort was reinforced by Williams teammate Alex Albon’s presence comfortably in the top 10.

Williams was seen as a dark horse heading into the weekend following a promising performance in pre-season testing.

Together with Alpine, it showed improved pace over a year ago prompting many to suggest the leading four teams had expanded to the top six.

Practice didn’t fill in that picture entirely, and it remains to be seen how genuine Sainz’s pace was, though it was a positive early start for a team more accustomed to appearing at the other end of the timesheets.

Alpine was absent, though Aston Martin showed stronger pace to ease some of the early concerns that plagued it during testing.

Doohan ended the session faster than his Alpine team-mate Pierre Gasly, the former 13th fastest and within a second of the outright pace.

Oscar Piastri was fourth fastest, his McLaren performing largely in line with expectations heading into this weekend’s Melbourne F1 event.

Red Bull’s Liam Lawson was only 16th best, the Kiwi building into the weekend with 22 laps – and a brush of the wall at Turn 9 – to his name.

Lewis Hamilton was 12th fastest on his Ferrari debut while a late moment for George Russell saw the new Mercedes team leader grab the grass at Turn 4 and spin in the dying moments of the 60-minute session.

The F1 field returns for a second hour of running at 16:00 local time.

Australian GP: Free Practice 1 Results