Lando Norris edged out title leader Kimi Antonelli in the final moments of the final practice session at the Mexico City Grand Prix.
The McLaren and Mercedes drivers were swapping between the top two positions throughout the running, before Norris set the pace by a narrow 0.001 seconds.
Charles Leclerc, who set the pace in both sessions on Friday, finished in third, with McLaren's Oscar Piastri in fourth.
Max Verstappen in the Red Bull was fifth-fastest. The Dutchman was complaining via the team radio, saying: 'they're just so terrible, these brakes.'"
Antonelli could seal the drivers' title this weekend by finishing Sunday's race ninth or higher. Although he wins regardless if Lewis Hamilton or George Russell do not win the race.
Hamilton crossed the line in sixth, nearly half a second off Norris' pace, while Russell was behind.
Verstappen will receive a one-place grid drop after being penalised for colliding with Liam Lawson during Friday's second practice.
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Verstappen's former Red Bull teammate Lawson, who was given the same penalty, is not yet confirmed to be driving for Racing Bulls next season and Verstappen said the incident was "not smart" for someone in the New Zealander's position.
Haas made a surprise announcement that Esteban Ocon had been replaced for the rest of the weekend by Ryo Hirakawa, but offered no explanation as to why.
Ocon took part in second practice on Friday, after Japanese driver Hirakawa had been given an opportunity in the first, but cut a frustrated figure after rowing with his race engineer during the session.
Qualifying for Sunday's Mexico City Grand Prix goes green at 9 p.m. BST / 5 p.m. ET.
Information from PA contributed to this report.
