Lewis Hamilton produced a surprise late show of pace to edge out Max Verstappen for the fastest time in opening practice at the Singapore Grand Prix.
Verstappen, who can win the world championship this weekend if results go his way, appeared to be continuing his dominant form for Red Bull as he topped the timesheet by a considerable margin for much of the session.
However, seven-time world champion Hamilton suddenly found significant improvement in his Mercedes in the closing stages on soft tyres, as he produced a 1:43.033 to top a practice session for the first time this season, with Verstappen second ahead of Ferrari's Charles Leclerc.
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With F1 returning to the Marina Bay Street Circuit for the first time since 2019 after the coronavirus pandemic saw the last two editions cancelled, the track produced its usual spectacular views along with several doses of drama.
Both George Russell and Lance Stroll hit the barriers, with the latter causing the first red flag of the weekend as he was forced to stop on track after a heavy collision with the wall on the way out of Turn 5.
Russell was fortunate not to suffer any significant damage as he had a gentler bump with a barrier after losing control at Turn 10.
Russell's struggles appeared to be part of a wider lack of pace for Mercedes, with Hamilton also having been off the pace until his late lap set up a possible three-way contest for pole on Saturday.
While Verstappen was within a tenth of Hamilton, Leclerc was four tenths back in third, but the Ferrari driver could have significant room for improvement after missing much of the first half of the session due to a brake issue, which became evident on his opening out-lap.
Each of the top three's team-mates appeared to be a step behind them, with Red Bull's Perez fourth, Russell fifth, and Ferrari's Carlos Sainz in sixth all in the region of a second back from Hamilton.
There was also an impressive return to action for Williams driver Alex Albon, who was back in the car less than three weeks after complications during laparoscopic surgery saw him placed in an induced coma.
Albon, who needed to be on a ventilator in the early stages of his recovery from respiratory failure, performed admirably on a circuit that is considered the sport's toughest physical challenge, finishing 16th, four places ahead of team-mate Nicholas Latifi.
Russell and Stroll were the only drivers to find the barriers, but several others had near misses, with Sainz remarkably avoiding the wall coming out of the final corner, and Verstappen also forced to recover from off track as he lost control in Turn 16.
Lando Norris, trialling significant new parts for McLaren, showed a concerning lack of pace as he finished down in 19th, almost a full second back from team-mate Daniel Ricciardo in 12th.
While Practice One began in daylight, Friday's second session, live on Sky Sports at 2pm, will reflect the night-time conditions that Saturday's qualifying and Sunday's race will be contested under, perhaps providing a more reliable pointer to where drivers stand going into the weekend.