George Russell in a Mercedes topped the timesheets Friday in the only practice session for the Singapore Grand Prix at a Marina Bay Circuit enveloped in smoky haze caused by fires in Indonesia.
Charles Leclerc's Ferrari was second on a dusty surface, with the McLaren of Lando Norris third as drivers and teams had just one hour-long session to maximise their set-ups before sprint qualifying later on Friday.
Singapore is featuring a sprint race for the first time and the only practice session took place before sunset, not ideal preparation for the Marina Bay Circuit's night race on Sunday.
Russell will start from the back of the grid for Sunday's race after taking a penalty for using too many engine components, but he can still compete for pole position in Saturday's sprint race.
The Englishman went round in 1min 32.274sec, 0.198sec ahead of Leclerc as the top five times were all set on the soft compound tyre, with Ferrari's Lewis Hamilton fourth and the second McLaren of Oscar Piastri fifth.
Max Verstappen, who won for the first time this season in Malaysia last weekend, was the fastest of the medium-compound runners in sixth, 0.732sec slower than Russell but half a second ahead of the other Mercedes of championship leader Kimi Antonelli.
Isack Hadjar of Red Bull was seventh fastest, followed by Pierre Gasly of Alpine and Liam Lawson in an RB who rounded out the top 10.
Verstappen has never won in Singapore, where extremes of heat and humidity play a part in the most physically attritional race of the season on a circuit notoriously difficult for overtaking.
HEAT HAZARD
Drivers can shed up to 3kg (6lb) during the race from sweating alone, and the race has been declared a "heat hazard" by organisers.
That means drivers can opt to wear cooling vests because the heat index is predicted to exceed 31C during either the sprint or the race.
The teams also have to contend with the smoggy haze, which saw Singapore's air quality plunge to an "unhealthy" 205 on Friday according to the IQAir tracking website.
Schools were shut in neighbouring Malaysia because of pollution from the wildfires raging in nearby Indonesia.
Readings above 150 are classified as unhealthy, while levels above 300 are considered hazardous.
Motorsport's governing body said the race was not under threat from the haze.
"Air quality levels are being monitored by the relevant local authorities and appropriate contingency measures are in place should conditions worsen," the FIA said in a statement to AFP.
The FIA added that some off-track activities and entertainment could be affected, but "based on the latest information available, air quality and haze are not forecast to represent a threat to track activity or the conduct of the event".