Red Bull's Max Verstappen set the pace in Friday's opening practice session for the Bahrain Grand Prix in Malaysia, posting the fastest lap as the four-time world champion seeks his first victory of the season.
Verstappen completed the 5.543-kilometer circuit in 1 minute, 37.520 seconds, finishing 0.383 seconds ahead of Mercedes' George Russell at the Sepang International Circuit, which is hosting the Bahrain race because of the ongoing conflict in the Middle East.
Verstappen's Red Bull teammate Isack Hadjar was third fastest, while Ferrari's Charles Leclerc was the only other driver to finish within one second of Verstappen's benchmark time.
"It's early to get excited because it's only FP1, but Max and Isack did a good job in very difficult conditions. They got into a rhythm pretty quickly," Red Bull team principal Laurent Mekies told Sky Sports F1.
"Everyone is fighting with the car because of the extreme heat, so it doesn't feel good for anyone."
Verstappen won the last Malaysian Grand Prix in 2017 before the race dropped off the F1 calendar, with the government saying it could no longer justify the costs.
Friday's session unfolded under sunny skies, though a dusty start-finish straight created hazy viewing conditions in the early stages.
Mercedes, which brought a new upgrade package to its car, arrived sporting a vibrant teal-green livery at the home track of its title sponsor, Petronas.
While Russell appeared to adapt quickly to the circuit, where he was driving for the first time, championship leader Kimi Antonelli could manage only fifth fastest, more than a second off the pace.
The Mercedes duo, separated by 66 points at the top of the championship standings, both encountered difficulties at Turn 4, going wide toward the end of the session as they grappled with tire-wear issues.
They were not alone in their struggles, with Ferrari's Leclerc, who last drove in Sepang in 2017 as a test driver, bluntly summing up the conditions by saying, "The tire degradation is insane."
His teammate Lewis Hamilton, who has one victory in Sepang, was sixth fastest, ahead of Alpine's Pierre Gasly. Racing Bulls drivers Liam Lawson and Arvid Lindblad, and Audi's Nico Hulkenberg completed the top 10.
The FIA said Hadjar, Lindblad and Franco Colapinto had exceeded their seasonal allowances for engines and that the three drivers received grid penalties.
Racing Bulls confirmed Lindblad was taking a fifth new power unit and would start at the back, while Colapinto received a 10-place grid penalty for exceeding his internal combustion engine allocation for the first time.
Colapinto had already been given a five-place grid penalty for causing the crash at Turn 1 in Baku, which took out teammate Gasly and McLaren's reigning champion Lando Norris.
Norris was only 12th fastest, behind his McLaren teammate Oscar Piastri.