Charles Leclerc went fastest in a practice session featuring 10 rookie drivers
Ferrari's Charles Leclerc led Mercedes driver Kimi Antonelli in first practice at the Mexico City Grand Prix, where the Italian is poised to clinch his first world title.
Leclerc was 0.659 seconds quicker than Antonelli, for whom a ninth-place finish will secure the championship regardless of any other results.
Only a victory by his team-mate George Russell or Ferrari's Lewis Hamilton can theoretically stop Antonelli becoming champion on Sunday. Even then, Antonelli only needs ninth place if Russell wins and 10th if Hamilton does.
Third quickest in the session was Mercedes reserve Frederik Vesti, driving Russell's car, ahead of Hamilton.
Mercedes were one of 10 teams to choose this session to do one of their mandatory rookie sessions. Only Ferrari had both race drivers in their cars.
Mexico City is chosen by many teams to run their mandatory rookie sessions because the first session is traditionally unrepresentative as a result of the dirty track surface.
Japanese Ayumu Iwasa, in for Max Verstappen at Red Bull, was fifth fastest, ahead of Alpine's Pierre Gasly and Aston Martin's Fernando Alonso.
McLaren's Oscar Piastri, Haas driver Oliver Bearman and Racing Bulls' Arvid Lindblad completed the top 10.
Briton Freddie Slater's first outing at a grand prix weekend for Audi did not go to plan. Reliability problems limited his running to 14 laps - about half a standard mileage. But he did manage to get out for the final 20 minutes or so and set the 19th fastest time.
He was just behind another Briton, Luke Browning having his latest run in the Williams.
Colton Herta, who Cadillac are considering promoting to F1 next year in place of Valtteri Bottas, was 22nd.
The team believe he has now done enough miles to secure the 40 points he needs to secure the superlicence required to run in F1.
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