Sainz's 1:36.857 put him more than 0.2s clear of Red Bull's Verstappen, with Lewis Hamilton a further couple of tenths back in third as Mercedes showed potential after bringing new upgrades to Texas.

The session at Austin's Circuit of The Americas had a fresh feel with five changes to the line-up - including four FP1 debutants - as teams fulfilled their young driver session obligations, with Ferrari's Charles Leclerc the most notable absence as Robert Shwartzman deputised for him.

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While several 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 Kevin 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.

Practice One took on additional importance with Friday's second session being a tyre test for Pirelli, meaning it will provide little data that will help team's for the remainder of the weekend.

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 take 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 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.