Germany arrived in Qatar among the pre-tournament favourites, but two Japan stars plying their trade in the Bundesliga, Ritsu Doan and Takuma Asano, both scored in the space of eight second-half minutes to put Hansi Flick's side on the verge of elimination after just one game.
Germany had taken the lead in the first period, Manchester City's Ilkay Gundogan coolly scoring from the penalty spot. And they had looked like easing to victory in the opening half, with the Japanese seemingly overawed by the occasion.
However, they failed to banish the ghosts of Russia 2018 - when, as holders, they exited at the group stage - as they proved incapable of pressing home their advantage, missing a plethora of golden chances.
Japan were reinvigorated in the second period, with Hajime Moriyasu freshening things up with a number of attacking changes which, ultimately, paid off as they brutally punished Flick's side for their failure to convert in the final third.
Manuel Neuer had made one brilliant point-blank save to keep Germany in front, but when he denied Taki Minamino from close range, the ball fell kindly for Doan, who couldn't miss from six yards in the 75th minute.
And eight minutes later, Asano, too hot to handle down the Japan right for much of the match, fired a rocket into the roof of the net to secure a stunning comeback win for a side who managed just 26 percent possession.
Here are five talking points from the Khalifa International Stadium...
1. First things first
Germany. Well done.
It wasn't the protest you wanted to make, but at least you came together, and found a way to make your point, unlike others.
This World Cup is becoming a political s***show thanks to FIFA's marching to the beat of Qatar's drum.
Let's see how they respond to this.
2. Musiala makes his stand
Jamal Musiala is a long-time friend of Jude Bellingham, the young duo having grown close while representing England's age-group sides before the Bayern Munich tyro switched allegiance to Germany.
Both have been tipped to make a major impression in Qatar, having shone for the respective club sides in both the Bundesliga and Champions League and England ace Bellingham certainly did just that in the Three Lions opener against Iran, with a tour de force at the heart of midfield.
Here, Musiala was at the centre of everything that was good about Hansi Flick's side. "A gorgeous footballer" declared Gary Lineker on social media and the BBC anchor wasn't wrong. The 19-year-old drew defenders close and span past them at will. He darted through minute gaps, flicked round corners, found gaps to play passes and create chances.
His only misstep was firing over after a wonderful virtuoso run into the Japan box had given him a golden opportunity to net his first World Cup goal. But that apart, this was another display to signal why those who watch him regularly are tipping the Bayern star to be a major player for club and country for the next decade.
Jamal Musiala was outstanding for Germany
3. Moriyasu gets it right... eventually
Hajime Moriyasu got this wrong early doors. Japan have a plethora of creative, technical players who need to be on the ball to show their best. They don't want to be chasing, chasing, chasing, giving up 70 percent possession and having to rely on rare attacks.
But that's what happened in the first period as they paid Germany too much respect. In a similar fashion to Wales against USA on Monday, they were far too stand-offish.
However, as the game progressed, and as his side grew in confidence, Moriyasu seemed to come to the realisation that, rather than sitting back and trying to counter, getting in the faces of this Germany side, closing down higher up the field, was the better bet. He married this with attacking substitutions and was repaid as Brighton's Kaoru Mitoma, ex-Liverpool man Taki Minamino and Freiburg's Ritsu Doan were all involved in the equaliser.
That caused delight. What happened next, caused delirium.
4. Let's talk about Asano
My word, what a first touch.
Takuma Asano had been a nightmare for Germany to handle throughout, his speed and movement from out to in down the right flank causing untold problems.
But the former Arsenal man - who never played a competitive game for the Gunners, unable to get a work permit - scored an absolutely unreal winner for the Blue Samurai.
Yes, he should have been offside because Niklas Sule should never have been two yards behind the rest of the defence. But when the long ball went over the top, Asano was on it in a flash and took down a difficult ball falling from the sky like Dennis Bergkamp in his prime. The touch ensured Nico Schlotterbeck couldn't get back and that Asano, even at a tight angle, was bearing down on goal.
And then, the finish. Neuer closed the angle, but the 28-year-old just rifled high into the roof of the net. An unerring, fantastic finish.
Takuma Asano of Japan celebrates ( Image: FIFA via Getty Images)
5. Oh, Hansi
Hansi Flick looked utterly furious after Japan made it 2-1.
He knows this was a nightmare result. Because, simply, it's Spain next.
It might well be cliche, but every match is a final for Germany now.