Mercedes scored its first front-row lock-out of the season to stun Red Bull in qualifying for the Mexico City Grand Prix.
Going into the session at the Autodromo Hermanos Rodriguez, Red Bull had dominated the second and final practice sessions, and it seemed odds on it would be they, and not Mercedes, who would be on the front row.
But Mercedes pulled out a qualifying display when it was most needed, with Valtteri Bottas claiming his 19th career pole position with a lap of one minute 15.875secs, finishing 0.145secs clear of team-mate Lewis Hamilton.
The seven-time F1 champion will not mind too much being second to Bottas given he now has both Red Bulls behind him, rather than in front, with Max Verstappen third on the grid ahead of team-mate Sergio Perez.
Hamilton, however, will start on the dirty side of the grid which may compromise him on the long run down to the first corner.
The suggestion going into and through qualifying was that Red Bull had an issue with the rear wings on both cars as they were being worked on just 10 minutes before the qualifying session began, and with tape clearly visible.
Whether that was detrimental is unclear but the team now faces a fight to get ahead of the Mercedes pair.
Aside from that, the final session was fascinating as the teams had realised the benefit of a tow down the long main straight provided a benefit of at least two- or three-tenths of a second.
Bottas emerged quickest in the first run by 0.145s over Hamilton after gaining a major slipstream from the Ferrari of Charles Leclerc, and that proved enough as none of the top four improved on their second runs.
Yuki Tsunoda in his AlphaTauri and McLaren's Lando Norris were ninth and 10th quickest, but the duo will drop to the penultimate row of the grid in 17th and 18th due to taking fresh power units.
Overall, it was a session that suffered a 26-minute delay in Q1 following a heavy shunt for Aston Martin's Lance Stroll as he exited Peraltada, the final corner.
Stroll appeared to be caught out by a snap of oversteer, forcing him slightly wide onto a dusty part of the circuit so when he applied the throttle it sent him into a spin and a significant shunt into a Tecpro wall.
Team principal Otmar Szafnauer said: "He's fine, a little bit unlucky that he ran a bit wide in the last corner. He just couldn't collect it."
Stroll was due to start on the last two rows given his power unit penalty but has now been guaranteed last on the grid following his accident.
That quartet, though, will all move up the grid due to the penalties for Tsunoda, Norris and Ocon.
In a Q2 that was spearheaded by Hamilton by 0.009s to Verstappen, Aston Martin's Sebastian Vettel qualified ahead of Alfa Romeo's Kimi Raikkonen, although the Finn faces a stewards' investigation over a pit entry incident in Q1 after Stroll's crash.
Williams' George Russell was 13th, but faces a five-place grid penalty for a gearbox change. The Briton, however, will only drop to 16th given the power unit penalties for this race.
Antonio Giovinazzi was 14th quickest, with Ocon 15th but the Frenchman will start 19th alongside Stroll on the back row.
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