The bemused and amused Spaniard, at his 150th grand prix weekend, asked his team over the race radio “no way, I didn’t expect that one... how did I do P1?” as he snatched pole off Verstappen on his last flying lap of the session.
Verstappen had a chance to wrest back pole but got held up in the second sector and had to make do with second in Sunday’s British Grand Prix.
The defending world champion had looked a class apart all Saturday having topped the practice times by nearly half a second and then the opening two qualifying sessions.
But in Q3 he spun dramatically and did well to save it on his first flying lap, and then skidded into the run-off area on his next attempt. It was a case of third time lucky as he clinched what looked like pole before Sainz’s superb lap, which Verstappen couldn’t better.
Afterwards, the Ferrari driver said: “In the end I put together a lap I didn’t think was anything special and it was pole position, which came as a bit of a surprise.
“The pace has been there all weekend. We should be in a good position to try to hold onto it.”
A number of teams arrived with expectations of a rise up the grid. Mercedes had arrived with their long-anticipated upgrade package of new front suspension, rear wing, sidepod and floor.
But while Lewis Hamilton briefly dallied with the front row of the grid he had to make do with fifth behind a second row of Charles Leclerc and Sergio Perez. Lando Norris was sixth with George Russell back in eighth.
The rain came down just moments before Q1 began, leading to a queue of cars lining up to be first on the grid on the intermediates before the rain got any heavier.
Valtteri Bottas was the only driver to spin in the opening qualifying run as Verstappen led the procession. It proved a dire session for both the Aston Martins and both Haas cars, neither making it through to Q2.
It led to remonstrations from Sebastian Vettel but also Alex Albon, in a Williams with a raft of upgrades hoping to take his team up the grid, behind teammate Nicholas Latifi in the older Williams.
It proved a qualifying to remember for Latifi, who made his way into Q3 for the first ever in his Formula 1 career.
If his appearance in the final session was a surprise, there were notable absentees in Daniel Ricciardo, supposedly safe in his job at McLaren next season but dreadfully off the pace of teammate Norris.
During Q2 as conditions worsened, there was a threat of Sainz missing out but he timed a lap just before the rain got any heavier. As the heavens opened again, Hamilton complained of tyre vibrations while teammate Russell bemoaned a lack of grip.
It proved a thrilling finale in Q3 with the lead changing hands before Sainz did enough for pole.