Ferrari started the Spanish Grand Prix weekend at the top of the timesheets, with Charles Leclerc setting the pace during first practice in Barcelona.
World Championship leader Leclerc worked his way down to a time of 1:19.828 on the Soft compound tyre to finish just under a tenth clear of teammate Carlos Sainz.
Max Verstappen finished three-tenths back in third, as Ferrari and Red Bull look set to continue their head-to-head battle this weekend.
Verstappen has cut Leclerc's championship lead to 19 points after back-to-back wins, with both of their teams running upgrades in a bid to steal a march.
Result Free practice 1 - Spanish
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Mercedes lead the 'best of the rest' battle
Mercedes, also armed with updates as they attempt to get on top of their porpoising issues, were the nearest challengers to the Ferraris and Verstappen's Red Bull.
George Russell posted the fourth-fastest time, the best part of a second off the pace, followed by Alpine's Fernando Alonso and teammate Lewis Hamilton.
McLaren, along with Aston Martin and Alfa Romeo, have brought one of the biggest upgrade packages to Spain, ending the session seventh and ninth with Lando Norris and Daniel Ricciardo respectively.
AlphaTauri occupied the other top 10 places, with Pierre Gasly eighth and Yuki Tsunoda 10th.
There were several new and returning faces throughout the one hour of practice, mainly thanks to F1's mandatory young driver sessions for 2022.
Robert Kubica got another run in the Alfa Romeo en route to 13th, Formula E champion Nyck de Vries (18th) outpaced Nicholas Latifi as he made his Grand Prix weekend debut for Williams, while Formula 2 racer Juri Vips (20th and last) appeared for Red Bull.
Huge drama off the track in Barcelona
Alongside the on-track action, there was plenty of drama off it as details of an FIA investigation into Aston Martin's upgrade package emerged.
Aston Martin have added various new parts to the AMR22 for this weekend's event, including a new floor body, fences and edges, and changes to the engine cover, cooling louvres, rear wing, sidepod inlets and Halo.
The modifications, particularly in terms of the sidepods and engine cover, immediately drew comparisons to the front-running Red Bull RB18.
After routine checks, a more detailed investigation was launched involving both teams, with Aston Martin ultimately cleared of any wrongdoing.
It remains to be seen whether there will be any fresh developments over the topic as the weekend - and season - develops.
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