They also made an unanswerable statement to that minority of us who believed that they had been praised too much, too quickly and with not much mind to a harder-nosed perspective.
What it said, quite beautifully and seamlessly and with, it seemed, an unlimited depth of facility was that sometimes history can – and should – wait.
We can never know how it would have gone if the prime of Real Madrid or Milan or Ajax had been resurrected and given today's science and fitness levels, and put in the place of an eviscerated United on Saturday night, when Ryan Giggs grew old before our eyes and Sir Alex Ferguson held up his hands in despair, but even the most sceptical were given one certainty that flew beyond a single caveat. It was that no football team could ever have seized a moment of its life so perfectly, with such touch and authority and – most impressive of all – a belief in its own ability and method that permitted no serious challenge.
Ferguson, in the depths of the disillusioning impact of a performance from Barça which he talked himself – and at least some admirers of his competitive instincts – into believing United could frustrate and, in their own way, match, advised that whatever the all-change culture of Spanish and Italian football his young conqueror, Pep Guardiola, should think very carefully about moving away to new terrain – and fresh opportunities to prove his ability.
The United manager said that Guardiola could never again expect to get greater rewards for his work and enjoy anything more in the rest of his football life than what had come to him now in the famous stadium. What precisely? Mostly, it was the superb triumvirate of Lionel Messi, Xavi Hernandez and Andres Iniesta.
Though there were other brilliant interventions, notably from Pedro and David Villa and Gerard Pique, it was again this Blessed Trinity of relentlessly creative footballers who put Barça on to another plane.
However brilliantly he worked in the future, Ferguson suggested, Guardiola could never guarantee himself quite such a core resource.
But again, this is history – and a piece of it Guardiola says he will be involved in for at least another season. It meant that what he had here was the force of a moment which would always have a life of its own, and this was along with the inescapable conclusion that it will take a lot more than the revived machinations of a Jose Mourinho to separate Barça from the belief that they are a big cut above any of their opposition.
For a Ferguson committed, at the age of 69, to making one last drive to restate his ability to build remarkably competitive teams, the ambition must have suddenly seemed a bit like being invited to climb Mont Blanc in his carpet slippers.
Certainly, his anticipated spending demands on the Glazer family could only have grown exponentially with every piece of evidence that Barça were operating on an entirely different level. The exhibits came in a torrent just as soon as United's opening burst of aggression was repulsed in an almost eerie reprise of what happened in Rome two years earlier.
The opening goal said everything about the chasm that existed between the teams. Xavi, who can rarely have played with quite such wonderful clarity of purpose and relevance, fired in the killer ball and Pedro's finish was worthy of the coolest matador.
Either side of Wayne Rooney's equaliser, what Xavi had done, and what Messi promised every time he got hold of the ball, plainly left United feeling that the best they could do was keep their heads above the waterline. Even such a modest hope was condemned to futility when Messi scored his first goal on English soil and then Villa unfurled his exquisitely flighted shot beyond a plainly unnerved Edwin van der Sar.
Barcelona's second-half authority was scarcely a surprise, given that Messi might have put his team back into the lead just before half-time with a move that unhinged even the superbly defiant Nemanja Vidic and Rio Ferdinand, but it was still stunning – and to no one more than the shell-shocked Ferguson. In the wreckage of one of his worst nights in football he admitted, quite plaintively, that Rooney's goal had given him a little hope.
He thought it might just embolden his team, give them at least a hint that by some device or other they might get back on terms with a team who had been unpicking them so effortlessly they could have been conducting a low-key seminar.
However, the United manager admitted that soon enough he knew a bitter truth. United couldn't control Messi, they couldn't staunch the myriad points of Barça inspiration that performed so many ambushes on the spirit of his team.
Beyond that inescapable reality Ferguson was aware of another one long before the end of the United debacle. It was that, if United can hope to think seriously of again being champions of Europe during his working lifetime, it will no longer be enough to pull off an inspired one-off swoop on a young player like Javier Hernandez. One of the many things Barcelona told Ferguson was that he needs more than piecemeal strengthening now; he needs a total renovation in that area of the field where Barça had everything and United, well, nothing.
The midfield was United's no-go area. Giggs, apart from his one effective moment when he supplied Rooney with the pass for his goal, simply could not get to the pace of the game. Antonio Valencia looked like a street busker who had wandered into the Royal Albert Hall. Park Ji-sung started with a roar but subsided into a whimper. Michael Carrick was, as in Rome, isolated and driven to distraction.
If the Glazers cannot see now the need for major investment, or are unable to produce it, they will have to submit to the judgement made long ago by so many United followers. It is that for them the club has never carried more implicit glory than that of a cash cow.
They have to accept that United's record 19th league title was not so much a step forward as a remarkably resilient refusal to fall back. If the men from Qatar want to revive their interest, they could not find a better time. Everything about Ferguson's demeanour said that the challenge facing both him and the club had rarely been so huge.
Barcelona had defined it quite specifically. They had condemned their victims to a lower order for some time at least – and there just wasn't any way around it, no more than there was the Barça midfield.
In the foreseeable future, football plainly belongs to Barcelona. They could not have annexed it more perfectly, more completely and, in Messi, they have a young champion against whom for some time there is unlikely to be a serious challenger.
What more can be said this side of some celestial play-off with the Real Madrid of Di Stefano and Puskas, the Milan of Baresi and Van Basten and the Ajax of Cruyff and Rudi Krol? Not much beyond the concession, that, sure, you would have to give Barça a shot.
The greatest ever?
* A third European Cup in five years has led to suggestions that the present Barcelona side is one of the greatest European club sides of all time, but they have some competition for that title:
* Real Madrid
Winners 1956, 1957, 1958, 1959, 1960
With Alfredo di Stefano and Ferenc Puskas at the peak of their powers, the Spaniards won the first five European Cups, the most mermorable a 7-3 final triumph over Eintracht Frankfurt in 1960.
Winners 1971, 1972, 1973
Led by the iconic Johan Cruyff, Rinus Michels/Stefan Kovac's side espoused the 'total football' mantra later taken up to great effect by the Dutch national team.
Winners 1977, 1978, 1981
Bob Paisley's team lifted three titles in five years, powered by a strong defence and domaneering midfield.
Winners 1989, 1990
With Marco van Basten leading the line and Ruud Gullit in his pomp ahead of a formidable defence, Arrigo Sacchi's team were the last to win back-to-back Cups.
Pique inspired by basket case
When Gerard Pique cut off the net from one of the goals to keep as a souvenir, TV pundit Gareth Southgate suggested he was collecting lace for a wedding dress for his girlfriend, Shakira. What he was actually doing was copying a basketball tradition, which began in the United States in the 1920s, whereby championship-winning teams cut off the nets from the hoops. Pique is likely to have got the idea from Barcelona's basketball side, who won the Euroleague title last season.
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