Lando Norris gave a significant boost to his championship chances by taking pole position for the Mexican Grand Prix while title rivals Max Verstappen and Oscar Piastri qualified in fifth and eighth respectively.
Norris is 14 points adrift of Piastri in the standings, but would move ahead of his McLaren teammate if the two cars finish where they start in Sunday's race.
His lap, which was 0.262 seconds clear of Charles Leclerc's Ferrari in second, also helps to counter the momentum of Verstappen, who has finished ahead of both McLarens at the last four races and is currently 40 points off Piastri.
No driver has won in Mexico after qualifying outside the top three since Alain Prost (13th) in 1990.
Reacting to his pole position on McLaren's team radio, Norris said: "What a lap, what a lap! Even I don't know how I did that ... The less I know, the better."
Norris' first task will be to fend off the two Ferraris of Leclerc and Lewis Hamilton, who qualified second and third, on the long run down to Turn 1.
Hamilton's qualifying performance was his best since joining Ferrari and he was just 0.090 seconds off teammate Leclerc.
George Russell qualified fourth for Mercedes and will start ahead of Verstappen in fifth and Kimi Antonelli in sixth.
Sainz qualified seventh but will drop to 12th after a five-place grid penalty for a collision with Kimi Antonelli at last weekend's U.S. Grand Prix is applied.
The penalty means Piastri moved one place up the grid from his qualifying result and will start seventh ahead of the Racing Bull of Isack Hadjar.
Haas driver Oliver Bearman secured his third Q3 appearance in as many races and will start 9th once Sainz's penalty is taken into account.
Under pressure Red Bull driver Yuki Tsunoda qualified 10th thanks to Sainz's penalty, but was 0.012 seconds off a place in Q3. Red Bull is expected to make a decision on Tsunoda's future after this weekend's race, and qualifying behind Hadjar -- the driver tipped to replace him next year -- will only have weakened his case for staying at the team.
Esteban Ocon qualified 11th and will start ahead of Sainz on the grid. The Sauber of Nico Hlkenberg secured 13th on the grid ahead of Aston Martin's Fernando Alonso in 14th and the second Racing Bull of Liam Lawson in 15th.
Gabriel Bortoleto will start 16th after qualifying his Sauber 0.121 seconds off a place in Q2. Alex Albon failed to make it out of Q1 for the fourth consecutive grand prix qualifying in a row after complaining of brake issues as he returned to the pits.
Pierre Gasly will start 18th for Alpine ahead of Aston Martin's Lance Stroll in 19th and the second Alpine of Franco Colapinto in last place.
