The Monegasque clocked a best lap in one minute and 17.166 seconds to beat the Spaniard by 0.067 seconds, leaving newly-crowned three-time world champion Max Verstappen third for Red Bull.
After dominating all three practice sessions, it was a surprise to see the 26-year-old Dutchman unable to stay on top as Ferrari found a surge of additional pace in the final Q3 section of qualifying.
Daniel Ricciardo was fourth for Alpha Tauri ahead of local hero Sergio Perez in the second Red Bull, seven-time champion Lewis Hamilton of Mercedes and Oscar Piastri of McLaren.
George Russell was eighth in the second Mercedes ahead of the Alfa Romeo pair of Valtteri Bottas and Zhou Guanyu.
Three of the top ten - Verstappen, Hamilton and Russell - faced stewards’ investigations for infringements during qualifying.
It is Leclerc’s fourth pole position success this year and the 22nd of his career, but he is without a win this season and has struggled to convert poles to wins.
Asked if he knew his car had the pace for pole, Leclerc said: "No, really. No I didn’t."
The session began in near-perfect conditions with an air temperature of 26 degrees Celsius and the track at 47 as Haas’s Kevin Magnussen led the way, but his early fastest lap was soon overhauled before Perez and then Verstappen took control.
The champion was half a second quicker than his Red Bull team-mate in the early exchanges as the times tumbled with some unexpected speedsters catching the eye, notably Ricciardo and Bottas for Alpha Tauri and Alfa Romeo, second and third with four minutes remaining in Q1.
In the thin air at an altitude of 2,250 metres, there were many nerves twitching in the closing minutes when Russell and Verstappen appeared to hold the field in the pit-lane, with only two minutes remaining.
They were delaying to time a perfect final lap as Alonso spun at Turn Three, prompting a yellow caution flag, while Lando Norris, who was expected to challenge for pole position was eliminated, unable to clock a hot lap in the final seconds.
The McLaren driver joined Esteban Ocon of Alpine, Magnussen, Aston Martin’s Lance Stroll – for the sixth consecutive race – and Williams Logan Sargeant in missing the cut to Q2.
Russell and Steward were both reported for investigation by the stewards along with Hamilton, for failing to slow under a yellow flag, and Russell, Norris and Alfa Romeo’s Zhou Guanyu faced a stewards’ call for running too slowly.
All this left the world champion, who topped Q1 ahead of Piastri, in command as he set the pace again in Q2 with Perez, to the dismay of his fans, struggling to keep pace.
For their second runs, the teams went out en masse, but slowly, while Verstappen stayed in the pits – to watch Hamilton go top. In 1;176.571, beating him by 0.054 seconds. Russell was third.
Zhou, Pierre Gasly of Alpine, Nico Hulkenberg of Haas, two-time champion Fernando Alonso of Aston Martin and Alpha Tauri’s Yuki Tsunoda initially failed to make the top ten cut until the stewards ruled that Williams’ Alex Albon’s best lap was deleted for exceeding track limits.
This dropped him to 14th and lifted Zhou back to 10th, a confusing move on a messy afternoon before Q3 even began. As it did, the Chinese was the only driver not to join the initial fray.
To a roar of delight, Perez led the way, clocking 1:17.788 but it was not enough to resist his rivals and after the first runs it was advantage Ferrari with Leclerc quickest ahead of Sainz and Verstappen with Ricciardo fourth ahead of Mercedes’ Russell and Hamilton.
Perez was seventh, hoping for a better second run as everyone went for new soft tyres for a final showdown.
