Red Bull driver Max Verstappen topped the opening Formula 1 free practice session for the Singapore Grand Prix, while Valtteri Bottas caused a red flag by crashing his Mercedes.
Verstappen used soft-compound Pirellis to knock Ferrari's Sebastian Vettel off top spot by 0.167 seconds with just under half-an-hour remaining of the 90 minute session.
Mercedes driver Lewis Hamilton had set the pace during the initial 40 minutes when drivers were on their first set of tyres, setting a time of 1m41.469s to lead the way by 0.469s.
During this phase of running, Racing Point driver Lance Stroll was third fastest, just ahead of Bottas who clipped a wall early on his run and damaged a rim - limiting him to just three early laps.
This meant Bottas was the first to head out on his second set of rubber, using hard-compound Pirellis first to move up to second then to take top spot.
Hamilton then headed out, also on hards, deposing Bottas by six tenths of a second to make it a Mercedes one-two.
But Ferrari still had to go and both Vettel and Charles Leclerc had fresh softs, with Vettel taking top spot with a lap of 1m40.426s.
Leclerc hit trouble before he could post a time on his fresh softs with a gearbox problem that manifested itself at Turn 19.
He was able to coast back to the pitlane, where his car was retrieved by the Ferrari crew - but did not return to the track.
Verstappen then improved again to take top spot for good with a lap of 1m40.259s, shortly before Bottas crashed and triggered a 10-minute red flag.
The rear stepped out on Bottas was he turned into the Turn 19 right-hander, sending him spearing into the wall with the car sustaining significant damage.
By this time, Bottas had been shuffled down to fourth behind Hamilton, with the second Red Bull of Alex Albon fifth fastest and 1.208s off the pace.
Nico Hulkenberg was the best of the midfield runners for Renault with a lap set on softs shortly before the red flag.
Both McLaren drivers were delayed by the red flag, but headed out after the restart to set their best times of the session - with Carlos Sainz Jr going seventh fastest, 1.746s off the pace.
Lando Norris went eighth, but only after an off at the Turn 7 left-hander while on his first push lap.
The two Toro Rossos rounded out the top 10, with Daniil Kvyat ninth and Pierre Gasly 10th and separated by just 0.072s.
Daniel Ricciardo was 11th fastest for Renault, just ahead of the lead Haas of Romain Grosjean - whose deal for the 2020 season with the team was confirmed on Thursday.
Alfa Romeo driver Antonio Giovinazzi was forced to have his quick run after the red flag, jumping up to 13th place with a lap 2.418s off the pace.
Stroll slipped to 14th by the end of the session having not improved on his first-set time due to moving onto hards, putting him just over three tenths ahead of the second Haas of Kevin Magnussen - who complained of braking problems early on.
Robert Kubica, who announced on Thursday that he will not continue with Williams next year, was 17th fastest ahead of Racing Point's Sergio Perez.
Leclerc ended up 19th with his early time ahead of the second Williams of George Russell.
Practice one times
|1||Max Verstappen||Red Bull/Honda||1m40.259s||-||22|
|5||Alexander Albon||Red Bull/Honda||1m41.467s||1.208s||24|
|7||Carlos Sainz Jr.||McLaren/Renault||1m41.966s||1.707s||20|
|9||Daniil Kvyat||Toro Rosso/Honda||1m42.305s||2.046s||26|
|10||Pierre Gasly||Toro Rosso/Honda||1m42.377s||2.118s||24|
|13||Antonio Giovinazzi||Alfa Romeo/Ferrari||1m42.677s||2.418s||15|
|14||Kimi Raikkonen||Alfa Romeo/Ferrari||1m42.786s||2.527s||13|
|15||Lance Stroll||Racing Point/Mercedes||1m42.791s||2.532s||28|
|18||Sergio Perez||Racing Point/Mercedes||1m43.369s||3.110s||23|