Ferrari drivers Carlos Sainz and Charles Leclerc each led a free practice session on Friday ahead of a United States Grand Prix that could seal Red Bull's first Formula One championship double since 2013.
Sainz was quickest in the first hour at Austin's Circuit of the Americas while Leclerc topped the timesheets in the extended 90-minute second stint that was mainly devoted to testing Pirelli's 2023 prototype tyres.
Red Bull's Max Verstappen, who wrapped up his second drivers' championship in Japan earlier this month, was second in practice one, 0.224 off the pace, with seven-time world champion Lewis Hamilton third for Mercedes.
Sainz's best lap was a one minute 36.857 seconds while Leclerc, who sat out the opening session while young development driver Robert Shwartzman made his race weekend debut, set a 1:36.810 in the afternoon.
The Monegasque did his best lap on this year's tyres, however, as one of a handful of drivers allowed to do half an hour of regular running to make up for missed time.
Alfa Romeo's Valtteri Bottas and McLaren's Daniel Ricciardo were second and third in that less representative second session with Sainz fourth.
Verstappen won last year in Texas and another victory with fastest lap on Sunday would secure Red Bull the constructors' crown with three races to spare. It would also equal the record for most wins by a driver in a single season, lifting Verstappen alongside Michael Schumacher and Sebastian Vettel on 13.
The champion was not entirely happy in the opening session, though, complaining that "there must be something wrong with the car because there is no front end in low speed".
Red Bull's Sergio Perez, who will have a five place grid penalty on Sunday for exceeding his engine allowance, was fifth in that practice.
Ferrari reserve Antonio Giovinazzi took the place of Kevin Magnussen at Haas in practice one but the Italian lasted barely eight minutes before he crunched into the Tecpro barrier to end his session.
Haas said the clutch was burned out and a gearbox change was likely before Magnussen returned for practice two.
"On your third lap to put it in the wall is not fantastic," commented team boss Guenther Steiner, who has yet to name Magnussen's team mate for 2023 with Mick Schumacher's future uncertain.
Five drivers replaced race regulars for the first session. They included 2021 IndyCar champion Alex Palou at McLaren in Daniel Ricciardo's car.
Shwartzman, who previously raced as a Russian in lower categories, was the fastest of the bunch in 16th place as stand-in for Charles Leclerc at Ferrari.
French teenager Theo Pourchaire was given track time by Alfa Romeo, ahead of a reserve role next season, while 21-year-old American Logan Sargeant drove for Williams while Canadian Nicholas Latifi sat out the session.
