Lewis Hamilton crashed into the wall twice and said "that's not what you expect from a champion" as Lando Norris secured a shock pole position for the Russian Grand Prix.
Norris, 21, usurped Hamilton as Britain's youngest ever pole-sitter with a scintillating lap in the wet-dry conditions at Sochi's Olympic Park.
On a superb afternoon for the country's rising Formula One stars, George Russell, who will join Hamilton at Mercedes next year, qualified third in his uncompetitive Williams machinery. Hamilton starts only fourth.
The performances by Norris and Russell, 23, provided a glimpse into F1's future on a day to forget for the grid's record-breaking superstar.
At a venue Mercedes have dominated – with seven victories in seven – Hamilton looked set to cruise to pole. But he inexplicably crashed into the pit wall ahead of his switch from wet to slick tyres.
The ensuing repairs in the final minutes of qualifying cost the 36-year-old valuable time in getting his dry rubber up to temperature.
He then fell off the track, sliding into the barrier, in the concluding metres of his last lap as Norris, Ferrari's Carlos Sainz and Russell sent him tumbling down the order.
"Ultimately I am incredibly disappointed with myself," said a dejected Hamilton. "I am really sorry for all the team here and back in the factory. That is not what you expect from a champion.
"These things are sent to try us but I feel terrible right now. Twice in the wall is very rare for me.
"It is nothing to do with the pressure of the championship. Mistakes do happen. It was embarrassing, but the problem with having the success that I have had is that anything but perfection feels like a long way off. I am only human."
Hamilton knows this is a race that he must take full advantage of with rival Max Verstappen, whom he trails by five points, propping up the grid following an engine penalty.
But the seven-time world champion, who has triumphed just once in his last 10 appearances, will have to fight his way past a McLaren, a Ferrari and a Williams for his 100th career win.
Norris, now in his third campaign, has been among the standout performers this year, and just a fortnight after claiming a career-best second at Monza, he clinched a debut pole and McLaren's first since Hamilton qualified at the front for the season-ending Brazilian GP nine years ago.
Hamilton was 22 when he took the first pole of his career in Canada in 2007. Norris celebrates his 22nd birthday in November.
"That's a pretty cool record," said Norris, who finished an impressive half-a-second clear of Sainz.
"I am now a part of history, and hopefully it never gets beaten. To knock anyone off is great, but it is cool that it was Lewis because he is the best driver in Formula One."
Norris also becomes the fifth-youngest pole-sitter in the sport's history, slotting in behind Sebastian Vettel, Charles Leclerc, Fernando Alonso and Verstappen.
How does he intend to celebrate? "I will call my mum and dad to say hello," he replied.
And what will he eat? "I am so nervous that I am not really peckish – probably not much, maybe an apple crumble with vanilla ice cream in the hotel," he added. "I had two last night so maybe I will have three this evening."
Qualifying appeared in danger of being scrapped after final practice was cancelled following a deluge of rain, accompanied by thunder and lightning.
But the poor weather eased in time, and dry conditions are forecast for Sunday.
Norris' nerve will be tested on the 350-metre charge to the first braking point.
He added: "Tonight I will study what happens if I get a good start, what happens if I have a bad start, how to defend, and how to get the guy in second place out of the dirty air because it is a long run down to turn two.
"It is not going to be easy to hold on because we are ahead of cars which are quicker than us but I am going to give it everything I have got."