Leclerc had previously set the same Q3 time as rival Max Verstappen, with both drivers achieving 1m 40.445s, but the Red Bull driver temporarily took the top spot.
But Leclerc fought back in the closing moments with a personal best first and last section, plus he ran faster than anyone in the middle of the lap, leading Verstappen by 1m 40.203s 0.188 seconds.
This was aided by Verstappen and his team-mate Sergio Perez falling short of their personal best times in the second period.
Leclerc said he was stunned by the team’s aim to beat Aston Martin and Mercedes ahead of the weekend as he takes his first pole position at Singapore 2022 and ends the season early broke the winning streak of Red Bull qualifying.
“I was surprised,” he said. “We went into the weekend thinking that if we qualified ahead of Aston and Mercedes it would be a good weekend and we ended up on pole so it was a real surprise.”
However, Leclerc did temper expectations for Sunday’s full grand prix as he conceded the RB19 could still outpace his SF-23 car.
He continued: “We can’t forget that our car might still be behind the Red Bull, so it will be difficult to stay ahead, but that’s the goal and really happy with the lap.
“It’s been a very challenging weekend for our drivers because there’s very little practice time (with the change to the sprint event schedule).
“We only had one practice session and then you have to go straight to practice, but it felt good from the start, really happy.”
Ferrari teammate Carlos Sainz is fourth behind Perez, and Leclerc added: “It will be challenging because we haven’t run medium (tire compounds).
“So tomorrow’s qualifying session (sprint) will be the first and we need to take part because we only have one set. So, there’s no room for error.
“But again, the pace seems to be strong. So, hopefully we can learn in Q1 and Q2 and then push in Q3, we know the car is good.”