World champion Lando Norris, who won last year's race from pole position, topped the times ahead of his probable successor Kimi Antonelli by just 0.001 seconds in Saturday's final practice at the Mexico City Grand Prix.
The 26-year-old Briton clocked a fastest lap in his McLaren in one minute and 17.600 seconds while the 20-year-old Italian recorded 1:17.601 for Mercedes. He finished ahead of Ferrari's Charles Leclerc as he bids to become the sport's youngest champion and Italy's first since 1953.
Leclerc was fastest in both sessions on Friday and topped most of FP3 on mediums before the teams switched to soft tyres.
Oscar Piastri was fourth in the second McLaren ahead of Red Bull's disgruntled four-time champion Max Verstappen, who complained his brakes were not working, seven-time champion Lewis Hamilton in the second Ferrari and George Russell in the second Mercedes.
Hamilton and Russell are the only drivers who can prevent Antonelli from taking the drivers' title, but only if one of them wins on Sunday and the Italian fails to finish in the top nine. Antonelli leads Russell by 123 points and Hamilton by 124.
Isack Hadjar was eighth in the second Red Bull, ahead of the two Racing Bulls of Liam Lawson and Arvid Lindblad
The session followed a hectic morning of paddock news, including Haas's decision to drop Esteban Ocon and bring in Japanese reserve driver Ryo Hirakawa, following the Frenchman's dispute with race engineer Laura Mueller on team radio on Friday.
In a statement, the team gave no reason for the switch but confirmed it was not because Ocon was ill.
GRID PENALTIES FOR VERSTAPPEN AND LAWSON
In another announcement, it was confirmed both Verstappen and Liam Lawson had been given one-place grid penalties for their tangle during FP2 on Friday, after which the Dutchman had criticised his stable-mate's "not very smart" behaviour. Both were also given a one-point super-licence penalty.
Isack Hadjar meanwhile received a formal warning by the International Motoring Federation (FIA) for brushing aside a paddock guest, who invaded his 'private space' on Friday morning.
Antonelli, enjoying himself despite the weight of expectation, and Ferrari pair joined the late fray and made an instant impact, the trio swapping fastest times on mediums with Hamilton, who missed the FP2 long runs with power problems, relishing his car's speed in the sunshine.
With 15 minutes remaining, Russell took softs and promptly went top ahead of Leclerc and Hamilton until replaced by Norris in 1.17.873, the first sub-1:18 lap of the day, before, on cue, Antonelli clocked 1:17.601 to jump almost three-tenths clear.
Norris and Piastri improved to go second and third before Leclerc overhauled them, but the young Italian stayed fastest by a tenth in a frantic finale until pipped by Norris by the narrowest of margins.
Alas, for the big crowd generating a carnival atmosphere, local hero Sergio Perez was ill and unable to clock a lap for Cadillac ahead of his 300th F1 race.