Valtteri Bottas denied Lewis Hamilton a 100th F1 career pole as Max Verstappen was third for Red Bull.
F1's top two teams opted for different tyre strategies for the final runs in Q3, with the Mercedes drivers returning to medium tyres with which they had dominated in Q2, and used to top qualifying at Portimao in 2020, while Verstappen stuck with the softs throughout.
But the tyre change did not work for either of the Black Arrows drivers, as Bottas's 1m18.38s that was set on the first Q3 runs on the softs ended up being the pole time.
Both Bottas and Hamilton could not improve on their final efforts, which meant the former's 0.007s advantage from the soft tyre runs gave him his first pole of 2021.
Verstappen had lost his first Q3 saving an oversteer snap to the right as he ran through Turn 4 and beyond the track limits onto the back straight and so was under extra pressure for the final runs.
The Dutchman was also only taking a single warm-up lap on the tricky low-grip surface compared to the two most other drivers completed.
Despite having to pass traffic on what would be his sole legal Q3 lap, Verstappen reached third but ended up 0.398s slower than Bottas.
Behind the leaders came Sergio Perez in the second Red Bull and Carlos Sainz, who outqualified Charles Leclerc for the first time as a Ferrari driver.
Esteban Ocon was sixth ahead of Lando Norris and Leclerc, with Pierre Gasly ninth for AlphaTauri.
Sebastian Vettel, making his first Q3 appearance since the 2020 British GP, took 10th for Aston Martin.
In Q2, the Mercedes and Red Bull drivers progressed through on the medium tyres as has become typical to start on the preferred rubber for the opening stint of the race, but here they were joined in this by Leclerc.
Both Ferrari drivers started Q2 on the mediums, but while Sainz switched to softs to ease his Q3 progression, Leclerc preserved with the harder rubber and did enough to get by with a personal best on his second flying run on the same set at the end of the end of the segment.
Behind the top 10 runners, George Russell took P11 for Williams, ending up 0.057s adrift of Gasly's P10 time in Q2 – crossing the line as the last of the runners setting flying laps in the middle segment.
Behind him came Antonio Giovinazzi for Alfa Romeo, ahead of Fernando Alonso and Yuki Tsunoda – the trio all completing personal best laps on their final Q2 runs but still being eliminated nevertheless.
Kimi Raikkonen could not improve on his final run and ended up P15 as a result in the second Alfa.
In Q1, Daniel Ricciardo suffered a shock exit ahead of Aston Martin's Lance Stroll, with Norris putting the other McLaren second in the opening segment, which featured Alonso spinning exiting the penultimate corner and Perez losing the rear running through Turn 4 and spinning through the gravel on the exit.
Ricciardo and Stroll not finding enough time on their final efforts in Q1 preserved Russell's perfect record of getting through to Q2 at all three races so far in 2021, as they failed to jump ahead of the Williams.
But it was Ocon's late jump to fourth on his last lap that meant Ricciardo could not progress.
At the back, Nicholas Latifi led the two Haas cars, with Mick Schumacher finishing ahead of Nikita Mazepin.
|3||Max Verstappen||Red Bull||1'18.746||0.398|
|4||Sergio Perez||Red Bull||1'18.890||0.542|
|5||Carlos Sainz Jr.||Ferrari||1'19.039||0.691|
|10||Sebastian Vettel||Aston Martin||1'19.659||1.311|
|12||Antonio Giovinazzi||Alfa Romeo||1'19.216||0.868|
|15||Kimi Raikkonen||Alfa Romeo||1'19.812||1.464|
|17||Lance Stroll||Aston Martin||1'19.913||1.565|