The 21-year-old, still seeking a first career win, was a massive 0.748 seconds clear of his four-time world champion team-mate.
The traffic in Belgium is terrible
Vettel grumbled about “traffic”, saying: “What a mess, what a mess, what a mess,” on the radio before swearing.
But in truth Leclerc was in a world of his own – Vettel had actually been 0.1secs quicker than his team-mate in the first sector of their final laps and Leclerc out-paced him by 0.4secs in the second sector and 0.2secs in the third.
And Vettel did not appear to have any more trouble with traffic than the other Ferrari.
All the top drivers were tripping over each other on their warm-up laps trying to ensure they got a slipstream, so powerful with these ultra-high-downforce, wide Formula 1 cars with their wide rear wings.
At one point Hamilton nearly crashed into his team-mate Valtteri Bottas, locking up his front wheels in the process.
Hamilton, whose team had a race against time to rebuild his car after a crash in final practice, lost out on a place on the front row to Vettel by just 0.015secs.
He said he was happy to have done so well after his earlier problems.
Hamilton said: “Ferrari have done a great job today; Charles did an exceptional job and I hope we can bring the fight to them tomorrow.”
What a lap by Leclerc
Leclerc’s advantage is his biggest over Vettel this season, in which he has been increasingly impressive. This is his third pole this season, and the sixth time in a row he has out-qualified the German.
“It obviously feels amazing,” he said. “It was very tricky, especially in Q3 I struggled quite a lot – the start of the lap was always very messy. But in the end I managed to do the rest of the lap OK. I did not expect to be that far ahead.”
Vettel said: “Messy. I was getting into a sort of rhythm, it took a little bit longer for me to get hold of the car but Q3 felt quite messy, a lot of queuing for the last corner, and the tyres then are not there where they are meant to be, but Charles did a better job today. “
Temperatures are expected to drop as much as 10C for the race, after a 29C high in the Ardennes for qualifying, and this could help Ferrari look after their tyres.
Leclerc said: “We have been quick since P1 but the race simulations in P2 we were not as quick so it is not going to be easy tomorrow. The gap is quite big today but it doesn’t mean it will be like that tomorrow, we will be working hard to improve the race runs and we see.”
Hamilton said: “It has been an interesting weekend. We struggled in the first sessions and I made a big mistake this morning – with the (set-up) change I made it didn’t feel that great.
“But the guys did an incredible job to perfection rebuilding it – I don’t ever want to put them in that position. I wanted to pay them back with a good qualifying session.
“Charles has been so quick all weekend but in the long run I am hoping we can at least give them a bit of a challenge. Hopefully we will be there or thereabouts and put in some interesting strategies.”
A good job by Albon
Alexander Albon did a strong job on his first outing for Red Bull following his promotion from Toro Rosso.
He did not attempt to get out of second qualifying because a penalty for using too many engine parts meant he was always going to start from the back of the grid.
But on the only lap he started in the second session before aborting it, he was only 0.3secs slower than Verstappen through the middle sector of the lap which features most of the corners.
That is a good start for the Anglo-Thai, especially because qualifying was the first time he had run the car on low fuel after focusing on race set-up throughout practice.
“It’s felt very different since P1 and it has felt more and more normal,” Albon said. “That was the first time on low fuel, there was a lot of downforce and I was enjoying that. The target was to get in the points and we have spent pretty much the whole weekend focusing on race runs.”
And Pierre Gasly, who was demoted from Red Bull and has taken Albon’s seat at junior team Toro Rosso for the remainder of the year, out-qualified team-mate Daniil Kvyat, despite only the Russian benefiting from an upgraded new Honda engine.
“A lot of things to discover and to reset my references from before,” Gasly said. “I am still learning a lot about the things I can do in this car. I don’t think we maximised the car in qualifying but considering we had the old engine compared to Dany, I think we did a decent job.”