It's absurd, of course, to say that one game can change history. Bayern Munich's 4-0 win over Barcelona on Tuesday did not end tiki-taka as a viable philosophy or devalue Barcelona as a club, nor did it suddenly install Bayern Munich as the dominant force in Europe for the next half decade. But some games do lie on the fault-lines of history and this felt like the moment at which, symbolically at least, Barcelona's star, waning for a little while, fell below that of Bayern Munich, which has been on the rise for some time.
Bayern were awesome, a blend of precise passing, pace and power. Their victory - even the margin of victory - was utterly deserved. There are just two sadnesses. The first is that their second and third goals should not have counted - even if it felt like a 4-0 game, it will always be 4-0 with an asterisk.
Both were shockingly bad decisions.
Mario Gomez may have been only a metre or so offside for the second goal but he was static, and the linesman even had the edge of the six-yard box as a guide; it's notable too that the initial reaction of both the fifth official and the Bayern coach Jupp Heynckes was to look to the linesman: they expected an offside call. The third goal was the result of a cynical block by Thomas Muller on Jordi Alba - again, so obvious it's hard to understand how it was missed. Against that, Bayern would argue they could have had three penalties for handball.
The second is how bad Barcelona were. This didn't feel like two giants going head to head, grappling in some epic contest; it felt like a much stronger team bullying a weaker one - both in terms of physicality and skill.
It seems bizarre that a side of Barcelona's standing should have become so reliant on Lionel Messi as to have to wheel him out when he is far from full fitness, their reliance highlighted by the fact that even as everything fell apart and discipline was lost, he was kept on, that he was still the player most likely to grab an away goal that might have kept hope alive. That speaks of a lack of a general tactical alertness - and that, indeed Barca's general predictability this season, may be the result of a lack of leadership. If Tito Vilanova has fully recovered from cancer, it may be that he can take a firmer grip next season.
The truth is that poor away performances are nothing new for Barcelona in Europe. Even under Pep Guardiola, their record in away knockout ties wasn't as good as might be assumed: last season they lost away to Chelsea in the semi-final and drew away to AC Milan in the quarter, the year before they drew away to Stuttgart and Arsenal and lost to Internazionale.
This season has been even worse: defeat away to Celtic in the group stage hinted all was not well, after which they lost 2-0 in Milan and drew 2-2 in Paris before Tuesday's debacle. The zip and the sense of invention of old have faded, while Barcelona's defensive shortcomings have been exposed.
The first two Bayern goals, not insignificantly, came from back-post crosses that were returned to the centre. Poor Gerard Pique, who seems to be expected to win every header, couldn't be everywhere. It's true that Barca were unfortunate to lose the centre-backs Carles Puyol and Javier Mascherano to injury, and then Adriano (although he is a full-back rather than a central defender) to suspension, but surely a club of their stature should have a back-up who is rather better than Marc Bartra. What, you wondered, has happened to Alex Song that he could not step in? And are Barcelona's back-up options at the back of midfield, having offloaded Seydou Keita (and before him Yaya Toure), so meagre that Sergio Busquets couldn't have stepped in alongside Pique?
Bartra, playing only his 22nd game for Barcelona, looked overawed and given his lack of experience it would be unfair to be too harsh on him, particularly as his task was made harder by the defensive inadequacies of both full-backs. Dani Alves and, to a lesser extent, Jordi Alba, aren't defenders in any traditional sense - they are almost deep-lying wingers, Barca's control of possession such that they rarely have to engage in any of the traditional arts of the full-back - and very occasionally, when they face an opponent who attacks them, that shows.
But those, frankly, are flaws we knew about, flaws inherent in the Barca model (and all models have them); it's just that previously teams were unable to take advantage. Bayern were good enough - and Barca poor enough - that they were exposed on Tuesday, but that is not to write off tiki-taka as a system, particularly given Bayern's style is essentially a slightly more direct version of the same philosophy.
It's not even to write off this Barca. History suggests that great teams, after a collapse of this magnitude, rarely recover, partly because a defeat like that suggests drive and confidence have already begun to diminish and partly because they are rarely allowed the chance to recover as personnel are changed. It's far from inconceivable that Barca could come back and win the Champions League next season but there are reasons for concern.
It's not so much that they are an old squad - although Puyol is 35 and Xavi 33 - than that playing together for a protracted period can lead to staleness. Again, that point hasn't necessarily arrived yet - although it has felt pretty close at times this season - but what is troubling is that integrating new players, outsiders who didn't grow up at la Masia, has proved difficult, particularly in more advanced positions: Alexis Sanchez and Cesc Fabregas have found it hard to adjust, while Zlatan Ibrahimovic never fitted in.
The modern economics of football mean that Barcelona will not fade away. Vilanova may reinvigorate them, and even if he doesn't they will lurk around the knockout stages and may one day catch a fair wind that will carry them, like Chelsea last season, to an unexpected success, but for this side, this generation, Tuesday's defeat felt significant. They remain a good team, a very good team, but the cycle has moved on. It is Bayern now, bristling with fine players enacting a thrilling style and buoyed by Germany's economic might, who wrestle with the possibility of greatness.