McLaren's Lando Norris pipped Mercedes' Kimi Antonelli by 0.001s in final practice for the Mexico City Grand Prix to set up a thrilling qualifying.
Ferrari's Charles Leclerc had topped both of Friday's practice sessions but McLaren and Mercedes showed their hand to outpace the Monegasque driver by one tenth of a second.
Antonelli is likely to become world champion in Sunday's race as he only needs a top-nine finish to secure the Formula 1 drivers' title.
McLaren's Oscar Piastri was fourth while Red Bull appear to be out of the pole position battle as Max Verstappen was 0.351s off the pace, but there seems to be a genuine three-team fight at the front for qualifying later on Saturday at 9pm (build-up from 8pm), live on Sky Sports F1.
Regardless of what he does in qualifying, Verstappen cannot start on pole position as he and Racing Bulls' Liam Lawson have a one-grid place penalty for colliding in second practice on Friday.
The stewards called the incident "unacceptable", with both drivers admitting the clash was "unnecessary and clumsy".
More drama took place before final practice on Saturday as Haas made the shock decision to replace Esteban Ocon with reserve driver Ryo Hirakawa for the remainder of the weekend.
The team provided no reason for replacing Ocon, but confirmed the Frenchman was not suffering from illness.
Haas recently confirmed that Ocon will be leaving the team at the end of this season after two years with the American-owned squad, with Brazilian youngster Rafael Camara signed as his replacement.
Hirakawa, a 24 Hours of Le Mans winner, has taken part in several practice sessions for Haas over the last two years and was 19th in final practice, six tenths down on team-mate Oliver Bearman.
Is anyone favourite for pole in Mexico?
Nobody delivered their best lap at the first time of asking in final practice on the soft tyre runs, leaving things even more open for qualifying given the teams usually optimise their setup and tyre characteristics to be quick on their first flying lap.
Leclerc visibly was sliding his car on most of his flying laps and it still feels Ferrari have more pace in the car, which neither driver showed in final practice as Lewis Hamilton languished in sixth ahead of Mercedes' George Russell in seventh.
"I think they can still be in the fight but it looked challenging [for Ferrari]," said Sky Sports F1's Jamie Chadwick.
"Both drivers, Charles in particular, those first few laps on the soft tyre is where it didn't really happen for them. I think that's the challenge, you have to be able to put the lap in when it counts.
"I think Ferrari's potential is higher, but it didn't feel like they managed to get the potential out of it early on the soft-tyre runs.
"I think they're still the dark horse favourites, or maybe not such dark horses, but I think it's gong to be so close between those top three teams."
Ferrari topped all three practice sessions last week in Austin before fading away in qualifying as Antonelli took pole position.
The Scuderia will hope a similar scenario does not repeat itself in Mexico City, with the added threat of McLaren being a force at the front for the first time in over a month.
Saturday October 31
5.15pm: Mexico City Grand Prix Practice Three (session starts at 6.30pm)
8pm: Mexico City Grand Prix Qualifying build-up
9pm: MEXICO CITY GRAND PRIX QUALIFYING
11pm: Ted's Qualifying Notebook
Sunday November 1
6.30pm: Grand Prix Sunday: Mexico City GP build-up
8pm: THE MEXICO CITY GRAND PRIX*
10pm: Chequered Flag: Mexico City GP reaction
11pm: Ted's Notebook
*also on Sky Sports Main Event
Formula 1 is in Mexico City where Kimi Antonelli could win the Drivers' Championship in Sunday's race at 8pm (build-up from 6.30pm), live on Sky Sports F1. Stream Sky Sports with NOW - no contract, cancel anytime
