Ferrari set the pace in Friday practice at the United States Grand Prix as Carlos Sainz and Charles Leclerc each topped a session in Austin.
Sainz's 1:36.857 put him more than 0.2s clear of Red Bull's newly crowned world champion Max Verstappen in Practice One, with Lewis Hamilton a further couple of tenths back in third as Mercedes showed potential after bringing new upgrades to Texas.
Leclerc, who was one of only five drivers able to do regular running in Practice Two having sat out the opening session as teams fulfilled their young driver session obligations, then went marginally faster than his Ferrari team-mate to top the timesheet.
- FIA makes offer to Red Bull after cost cap breach | Max: Rivals 'hypocritical'
- FIA: Suzuka recovery vehicle should not have been deployed
- United States GP: On and off-track drama all live on Sky Sports
Practice Two at Austin's Circuit of The Americas was used for Pirelli to test 2023 prototypes, with drivers unable to make setup changes as they tried out unmarked compounds while performing running plans set by F1's tyre manufacturer.
However, Leclerc, along with Valtteri Bottas, Daniel Ricciardo, Kevin Magnussen and Nicholas Latifi, was allowed to do 30 minutes of running at the beginning of the extended 90-minute session, during which the Monegasque backed up his team-mates' strong FP1 performance.
The opening session had a fresh feel with five changes to the driver line-up - including four FP1 debutants - with Leclerc the most notable absence as Robert Shwartzman deputised for him.
While the new faces enjoyed their first F1 experience, Antonio Giovinazzi spurned his opportunity to put himself in contention to drive for Haas next season as he crashed Magnussen's car in the opening stages, triggering a red flag and causing damage that ruled him out of the remainder of the session.
Lance Stroll was fourth in another encouraging display from Aston Martin, beating the second Red Bull of Sergio Perez to fifth.
Ferrari academy driver Shwartzman was joined by fellow youngsters Alex Palou (McLaren), Theo Pourchaire (Alfa Romeo) and Logan Sargeant (Williams), but it was the relatively experienced Giovinazzi who made a rookie error.
Just a few minutes into the session, the 28-year-old Italian spun at Turn 6 before running off into the barrier. He initially appeared to be stuck there as red flags were waved, but eventually got moving and was able to get the car back to the Haas garage.
However, clutch damage prevented him from getting back out on track, and most likely ended his hopes of challenging Mick Schumacher for his seat with the team next season.
Verstappen, who sealed his second successive title - with four races to spare - by winning in Japan earlier this month, looked to be continuing his dominant form as he set the pace as soon as the session resumed.
Hamilton had spoken on Thursday about his hopes that Mercedes' upgrades could bring them closer to Red Bull, but the initial signs were negative as he and team-mate George Russell remained four seconds off the pace for the first half of the session.
However, when the seven-time world champion switched to soft tyres, he immediately closed to within a couple of tenths of Verstappen, while Russell - who finished seventh - was almost half a second slower.
But then came Sainz, as Ferrari showed strong Friday speed once more, jumping six tenths clear of Verstappen. The Dutchman attempted to respond but was left frustrated after being unable to threaten the Spaniard's time.
"There must be something wrong with the car because I have no front end and low speed," Verstappen said over team radio at the end of the session.
It was confirmed during the session that Red Bull's Perez and Alfa Romeo's Zhou Guanyu will receive five-place grid penalties in Sunday's race after taking new engine parts, while Ferrari have admitted both of their drivers are likely to take new parts that will also drop them down the grid.
The penalties appear likely to help Red Bull seal the constructors' championship, with Ferrari needing to best the leaders by 19 points to extend the contest to next weekend's Mexican Grand Prix.
The penalties could also have an impact on the battle for second in the drivers' championship, with Perez currently leading Leclerc by just a point.
The US GP weekend began in the shadow of F1's ongoing cost cap saga, with the paddock awaiting an announcement on how Red Bull will be punished for breaching the 2021 spending limit.
Red Bull chief Christian Horner is set to face the media in the team principals' press conference on Saturday at 5:25pm, live on Sky Sports, with the F1 community eagerly awaiting an update on the situation.
Given the limited running available on Friday due to the tyre test, Practice Three is likely to take on additional significance on Saturday ahead of Qualifying, with both sessions live on Sky Sports F1, at 8pm and 11pm respectively.