George Russell finished fastest in first practice for the Azerbaijan Grand Prix after team-mate Kimi Antonelli broke down with a mechanical failure.
Antonelli heads into Saturday’s 15th round of the season in Baku holding an 81-point lead over Russell in the championship standings.
However, Antonelli was forced to withdraw midway through the one-hour running as gremlins struck his Mercedes.
The Italian pulled over to the side of the road reporting a loss of hydraulic pressure.
Antonelli was top of the time sheets after the initial laps on the hardest compound, but he was fifth by the end of the session as his rivals bolted on the speedier soft tyres.
And it was Russell who took advantage of his team-mate’s demise to set the quickest time, four tenths faster than Max Verstappen’s Red Bull.
Although it was not all plain sailing for Russell after he ran off the road under braking for the fourth corner before he safely returned to the street track.
Charles Leclerc finished third, 0.404 seconds slower than Russell, with Lewis Hamilton a place back in fourth.
Antonelli completed just nine laps and his Mercedes mechanics will be left to repair his car for the day’s second running later on Thursday.
Isack Hadjar is back in his Red Bull cockpit having missed the past three races with a wrist injury.
The Frenchman renewed terms to stay at Red Bull for next season but he was able to complete just eight laps after he suffered an engine problem.
Elswhere, Oscar Piastri finished sixth for McLaren, a place clear of Liam Lawson, now back at Racing Bulls, after he deputised for Hadjar in Zandvoort, Monza and Madrid.
Lando Norris was only 14th at a venue he expects will not suit his McLaren. Second practice gets under way at 16:00 local time (13:00 BST).
