Leclerc ultimately lapped only 0.139 seconds shy of polesitter Max Verstappen in the final part of the shootout, with the Red Bull driver failing to improve on his last flying lap.
It marked a quick recovery for Leclerc, who was only ninth after his first run in Q3. He reckoned his driving was on the money but that the car had let him down in a straight line.
He felt as though the "peaky" SF-23 then came alive when fresh tyres were fitted, leaving him with a "big surprise" as he jumped up to second place.
Leclerc said: "For some reason, again, our car is very peaky so whenever we are on scrubbed tyres, like the first run in Q3 was a very good lap, but we were last.
"I didn't have many hopes. But then when we put on the new tyres, everything comes alive.
"It felt great. Again, I did a great lap. Really happy to be on the front row. But it's a big surprise."
Leclerc thought he was at risk of dropping out of qualifying in Q1 and Q2 before progressing into the top 10 shootout and capitalising on a large final-sector slide that knocked McLaren's Lando Norris out of contention for pole.
The Monegasque continued: "Honestly, considering the weekend we've had until now, I did not expect it at all, the last lap. I knew I had to put absolutely everything together.
"I did the last corner, was a bit too much sliding. But I think everybody has had that.
"Q1 and Q2, I was worried to go through and at the end a front row, so it's amazing."
Leclerc did suggest his priority for the race was to consolidate second position rather than take the fight to Verstappen, with Ferrari needing to focus on jumping Mercedes for second in the constructors' championship.
The Scuderia sits four points adrift entering the final race of the season.
"I hope it's going to go well," said Leclerc. "That's the target. It is to beat [Mercedes] in the constructors' championship.
"I really hope Carlos [Sainz, eliminated in Q1] can have a great start and then join me in the fight.
"Let's try and put both of our cars in front of both Mercedes [George Russell fourth, Lewis Hamilton 11th] and come back home with a second place in the constructors'. That is all that matters to me this weekend."
