Carlos Sainz kicked off the United States Grand Prix by finishing fastest in first practice at the Circuit of the Americas.
The Ferrari driver finished quicker than new double world champion Max Verstappen, who was on a faster lap before running wide at the penultimate corner.
Lewis Hamilton finished third for Mercedes as the team debuted a new upgrade package on the W13.
But the star of the hour was former IndyCar champion Alex Palou, making his FP1 bow for McLaren.
The session was full of on-track action ahead of the 2023 prototype Pirelli tyre test in FP2.
Antonio Giovinazzi was one of five drivers making a substitute FP1 outing, but the Italian caused a red flag on his return to an F1 cockpit when spinning at the esses in the first 10 minutes.
The Haas was left with damage to the front wing and the bodywork on the right-hand side, as well as around the rear-wheel assembly but although initially jamming in the barriers, Giovinazzi was able to squirm free and return the VF-22 to the pits.
The clutch had overheated and the team confirmed a gearbox change was likely, ending Giovinazzi's session.
Robert Shwartzman, making his debut F1 race weekend outing for Ferrari, missed out on some 10 minutes of running early on due to discomfort in the car with the Scuderia forced into cockpit changes.
The remainder of the session saw a mixture of run plans as teams pushed to make the most of the first hour of running, knowing the second practice session will see focus switch to the tyre test.
Ferrari would have been concerned by a piece of bodywork flying away from Carlos Sainz's car midway through the session as the Spaniard bounced its way through the esses, proving the vigour of the bumps despite resurfacing work at COTA.
Soft tyre qualifying runs came late in the session, with drivers pushing the limits of the circuit.
Max Verstappen was looking like he would take the fastest time of the session before running wide at the penultimate corner, whilst Sebastian Vettel did well to hold a slide at turn nine.
That meant that Sainz finished fastest with a time of one minute 36.857, two-tenths faster than Verstappen.
Hamilton was a further two-tenths back in third ahead of Lance Stroll, who impressed for Aston Martin as the team looks to continue its strong form of late.
Sergio Perez finished fifth in the second Red Bull, fresh with the news that the Mexican will take a five-place grid penalty for taking on a new ICE.
Fernando Alonso, George Russell, Pierre Gasly, Lando Norris and Vettel rounded out the top 10.
Norris' team-mate for the session Palou starred and although finishing only 17th, the Spaniard did not run the soft tyres at the end of the session.
Palou was aggressive from the start and was only three-tenths off Norris' pace on the medium tyres, before the Briton made the swap to soft tyres.
The fastest of the rookies was Shwartzman, who finished 16th and two seconds slower than team-mate Sainz. But the Israeli-licenced driver was held up by Verstappen on his best lap and lost around half a second in the final corner.
Théo Pourchaire didn't put a foot wrong behind the wheel of Valtteri Bottas' Alfa Romeo, neither did Williams' American development driver Logan Sargeant, though both drivers were off the ultimate pace as they became accustomed to the machinery.