Charles Leclerc led the way in first practice for the United States Grand Prix as Kimi Antonelli's quest to claim the title in Texas got under way.
The Monégasque led Max Verstappen by 0.084 seconds in the first running on Friday, with Lando Norris over two tenths back in third.
Runaway championship leader Antonelli could seal the championship this weekend and become Formula 1's youngest ever champion.
His chances of doing so are unlikely; he would need to win Sunday's race at the Circuit of the Americas and for George Russell to be lower than ninth and Lewis Hamilton lower than fifth.
The Italian, 20, has a 102-point lead with six scheduled rounds remaining -- making his march to the crown merely a matter of time. He was fifth in first practice, one place below Russell.
Verstappen is bidding for three wins in a row this weekend, after success in Malaysia and Singapore, as the four-time world champion looks to end a difficult season with momentum.
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Hamilton, a record five-time winner around this circuit on the outskirts of Austin, was over five tenths behind teammate Leclerc in sixth.
Oscar Piastri in the other McLaren finished behind, with Audi's Gabriel Bortoleto in eighth.
Second practice gets under way at 10 p.m. BST / 5 p.m. ET.