George Russell went fastest for Mercedes as 10 Friday drivers took part in Practice 1 at the Abu Dhabi Grand Prix.
Under the regulations, all teams must run a reserve and development drivers in two FP1 sessions during the season.
With Yas Marina the last chance to meet that requirement, AlphaTauri was the only team not to run a revised line-up, while Red Bull had juniors in both their cars, as Jake Dennis and Isack Hadjar replaced Max Verstappen and Sergio Perez.
Unsurprisingly, the regular race drivers dominated the top 10 early on, with George Russell setting the pace for Mercedes on mediums.
Bouncing was a big topic early on as teams conducted aero tests and pushed ride height levels, leading to grounding through Turns 2 and 3 in particular.
Alpine reserve Jack Doohan had a near-miss against a slow-moving Logan Sargeant between the final two corners, with the Aussie having to take major avoiding action to prevent a high-speed crash.
A slippery final corner provided plenty of slides as drivers scrambled for grip on the exit.
Drivers switched onto soft tyres just after halfway with Russell continuing to set the pace on a 1m26.072s.
Aston Martin reserve Felipe Drugovich jumped upto second, less than three-tenths behind the Mercedes.
Daniel Ricciardo took third for AlphaTauri, pipping Valtteri Bottas in fourth by just 0.02s.
Lance Stroll claimed fifth in the second Aston Martin but was involved in a late incident with Hadjar at Turn 6, forcing the Red Bull junior off the track to avoid the Canadian.
Oscar Piastri sat P6 ahead of the two Ferraris of Carlos Sainz and reserve Robert Shwartzman, who was just 0.027s slower than the Spaniard.
Pierre Gasly finished ninth and Yuki Tsunoda completed the top 10.
Sargeant was 11th, ahead of Mercedes junior Frederik Vesti in 12th. Doohan took 13th for Alpine, ahead of F2 championship leader Theo Pourchaire in the Alfa Romeo.
IndyCar star Pato O’Ward claimed P15 in the McLaren with Dennis and Hadjer 16th and 17th for Red Bull.
Jak O’Sullivan took 18th for Williams as Kevin Magnussen and Oliver Bearman brought up the field for Haas.