Pierre Gasly topped the timesheet for AlphaTauri in the first practice session of the new Formula 1 season, as Lewis Hamilton was only seventh for Mercedes ahead of Sunday's Bahrain Grand Prix.
Gasly recorded a 1:34.193 to lead the Ferraris of Charles Leclerc and Carlos Sainz in the day-time heat of Sakhir, while the other Mercedes of George Russell was fourth, with world champion Max Verstappen fifth for Red Bull.
The drivers will return to the track for the second practice session in the Bahrain evening (3pm GMT), when track conditions will be more representative of those the teams will face in Saturday's qualifying and Sunday's race.
There was a continuation of the form that had been shown in pre-season testing at the same track last week, with Ferrari and Red Bull appearing a step ahead of Mercedes.
After an early interruption to the session caused by the sudden shattering of a sidepod on Esteban Ocon's Alpine, Red Bull, who produced a hugely impressive showing on the final day of testing last weekend, went to the top of the timesheet with Verstappen ahead of team-mate Sergio Perez.
Russell provided some encouragement for Mercedes as he briefly went fastest, albeit using a softer (and faster) tyre than the Red Bulls.
However, Gasly, also on the softer tyre, soon usurped him, with the Ferraris, using the same medium tyre as Verstappen, then slotting in behind the AlphaTauri to maintain the consistency they've shown throughout the pre-season.
Despite finishing behind the Aston Martin of Lance Stroll, there appeared to be possible cause for consolation for Hamilton, with Sky Sports F1's Ted Kravitz explaining during the session that the seven-time world champion was trying out an alternate floor on the W13.
Hamilton was running extra parts on his floor to collect data, which when removed could allow the Mercedes to go faster, as the team continues to battle the uncomfortable bouncing motion - also known as porpoising - that has hampered their pre-season.
Until the teams fully unleash their cars for qualifying on Saturday it will be impossible to fully gauge who has the most pace, but Friday's P2 session under the lights is likely to provide more clues with qualifying simulation runs expected.
While the top 12 were all within a second of the leading time, there was a concerning lack of pace for McLaren, with Lando Norris and Daniel Ricciardo 16th and 17th respectively, following brake issues last week.
Alpine appeared to recover from their early setback after restoring an older iteration of their sidepods on both cars, with Fernando Alonso finishing eighth and Ocon 12th.
There were more technical issues for Alfa Romeo, with Valtteri Bottas the only driver that failed to set a lap time as he reported "misfiring" early in the session. However, his team-mate, Chinese rookie Zhou Guanyu, completed a very healthy 20 laps and finished 11th.
Stroll's sixth-place - ahead of Hamilton and the other Red Bull of Perez in 10th - will provide encouragement for Aston Martin. Nico Hulkenburg, stepping in for Sebastian Vettel, who has Covid-19, split the Williams of Nicholas Latifi and Alex Albon to finish 14th.
That performance - and solid lap counts for both drivers - capped an improved session for Williams, who comfortably outperformed back-field rivals Haas, with Mick Schumacher and Kevin Magnussen last among those who completed times.
Bahrain GP live schedule on Sky Sports F1
Friday, March 18
2.45pm: Bahrain GP Practice Two (session starts 3pm)
4.20pm: F2 Qualifying
5pm: The F1 Show: Bahrain
Saturday, March 19
9.55am: F3 Sprint Race
11.45am: Bahrain GP Practice Three (session starts 12pm)
2pm: Bahrain GP Qualifying Build-up
3pm BAHRAIN GP QUALIFYING
4.35pm: F2 Sprint Race
5.35pm: Ted's Qualifying Notebook
Sunday, March 20
8.55am: F3 Feature Race
10.35am: F2 Feature Race
1.30pm: Grand Prix Sunday: Bahrain
3pm: THE BAHRAIN GRAND PRIX
5pm: Chequered Flag: Bahrain
6pm: Ted's Notebook
7pm: Bahrain GP Highlights
Many of our shows will also be simulcast on Sky Sports Main Event and Sky Sports Mix.
All of Friday's live action can be watched on Sky Sports Main Event, while Saturday's qualifying will be on the channel from 2.45pm, as well as the F2 Sprint Race (4.35pm) and Ted's Qualifying Notebook (5.35pm).