Ferrari's Charles Leclerc headed McLaren's Lando Norris in Friday practice at the Mexico City Grand Prix.
Mercedes driver Kimi Antonelli, who is poised to clinch his first world title on Sunday, was fourth fastest behind team-mate George Russell.
Only a victory by 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.
Leclerc, who topped both sessions on Friday, was 0.103 seconds quicker than Norris, with Russell just 0.003secs further adrift.
Antonelli was 0.217secs off the pace, and ahead of the Red Bulls of Max Verstappen and Isack Hadjar.
Leclerc's team-mate Lewis Hamilton was 11th overall after stopping on track with a technical problem before completing his qualifying simulation runs on the soft tyre.
Behind Hadjar, Racing Bulls duo Arvid Lindblad and Liam Lawson sandwiched Pierre Gasly's Alpine, while McLaren's Oscar Piastri completed the top 10.
Verstappen and Lawson face a trip to the stewards after a collision in the stadium early in the session.
The first session was marked by 10 of the 11 teams running 'rookie' drivers in their cars.
One of them was Cadillac's Colton Herta, who the team are considering promoting to a race seat in place of Valtteri Bottas next season.
Initially, the team felt his running in Mexico had given him enough points under the F1 system to earn a 'superlicence', which is required to race in F1.
But further investigation by governing body the FIA revealed the American nine-time Indycar race winner is still one point short and will have to complete one further practice session this year to secure his licence.
The team plan to do that before the end of the season.
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