Red Bull’s Max Verstappen led Ferrari’s Sebastian Vettel in an unrepresentative first practice session at the United States Grand Prix.
The order was mixed after many drivers spent time trying out a 2020 Pirelli development tyre.
Verstappen’s quickest time was set on the standard ‘soft’ tyre, while Vettel ran the test tyre for his best lap.
Lewis Hamilton, poised to clinch his sixth world title this weekend, was down in eighth place in his Mercedes.
Hamilton, who was 1.382 seconds off the pace, will win the championship this weekend as long as team-mate Valtteri Bottas does not win the race and the Briton finish lower than eighth.
Vettel’s team-mate Charles Leclerc set the second-fastest time but had it deleted for exceeding track limits at Turn 19.
That was on the ‘standard’ soft tyre and the 22-year-old was left to rely on his best lap on the 2020 tyre for his sixth place.
Leclerc was behind Toro Rosso’s Pierre Gasly and Renault’s Daniel Ricciardo and ahead of the Racing Point of Lance Stroll and the second Toro Rosso of Daniil Kvyat.
A number of drivers complained about the bumps on the Circuit of the Americas.
Hamilton, who says it is one of his favourite tracks, said: “This must be the bumpiest track in the world.” And Haas driver Kevin Magnussen described “a jump – not a bump – at Turn Nine”, which was causing part of his hybrid system to cut out.