By Phil McNulty
Chief football writer
Manchester United's exit from the Champions League - the first time they have failed to reach the quarter-final in eight seasons - sent shock waves around Old Trafford.
Sir Alex Ferguson can rightly point to the ill-fortune of conceding a last-minute goal against Porto and the perils of an horrendous decision from a linesman that ruled out a potentially decisive second goal from Paul Scholes.
But the late winner has been United's stock in trade through their glory years - just ask Bayern Munich and many other victims - while blaming an official would only disguise a painful truth about United's demise.
And that is the brutal fact that the calamitous setback against Porto was an accident that has been waiting to happen to Manchester United all season.
This is why.
THE DAVID BECKHAM DEAL
Ferguson loves horse-racing - so he will have known he was taking a gamble by allowing one of Old Trafford's thoroughbreds to leave and join a stable that could arguably be regarded as United's biggest European rival.
Beckham's time at United appeared to have become a misery, with Ferguson sick of his celebrity lifestyle and more than happy to see him leave.
Beckham has not been truly replaced
The deal was tacitly accepted by supporters on the basis that their trust in Ferguson was implicit as a result of his success and that he already had a ready-made replacement in the bag... didn't he?
Beckham was regarded as something of an under-achiever in his closing days at United, but what would they have given for him against Porto?
THE SUMMER TRANSFER MARKET
Ferguson appeared to pin all his hopes on securing Brazil's brilliant World Cup winner Ronaldinho from Paris St Germain as a player who could provide the profile, glamour, inspiration and football fantasy to replace Beckham.
After a tedious summer saga, Ferguson uncharacteristically missed out on his prime target as Ronaldinho joined Barcelona.
The charismatic forward's form in Barcelona's La Liga resurgence is leaving United with serious cause for regret.
It left Ferguson with money to spend, and after missing out on the jewel in Brazil's crown he decided to have a punt on a few unpolished gems.
Cameroon midfielder Eric Djemba-Djemba arrived from Nantes but has struggled to cope with the Premiership and Europe's demands.
Kleberson was also a Brazil World Cup winner, but Beckham or Ronaldinho he is not and he was left on the bench on Tuesday.
Ronaldinho deal was scuppered
Cristiano Ronaldo appeared to be Ferguson's idea of Beckham's natural replacement at £12.5m, the Scot even handing him the prized number seven shirt.
Ronaldo is something of a show pony who needs the rough edges knocking off, understandable in a teenager, but he is very much one for the future and was not trusted with a starting place against Porto.
Unknown American goalkeeper Tim Howard arrived from Metrostars to replace Fabien Barthez and has looked a real find for most of the time.
But the edges have frayed as United's form has fluctuated and he made a basic error for Porto's equaliser.
Howard deserves a measure of sympathy because, in reality, he lacks experience at the top level, certainly in coping with the pressure points of the Champions League.
So Ferguson, having lost a major world star, filled the gap with bit-part players.
He built for the future when the present needed more urgent attention - and has paid an expensive price.
THE FOLLY OF ROY KEANE
The influence of captain Roy Keane was sorely missed against Porto, but United can have no complaints because it was all the result of their captain's crass stupidity.
Keane, so willing to lecture team-mates, showed gross irresponsibility to stamp on Porto keeper Vitor Baia in the first leg in Portugal.
Ferguson claimed it was not in Keane's nature to be malicious. Sorry, Sir Alex - just study his record, or if you're still not sure read the passage in his book about Alf-Inge Haaland.
If United were hurt by Keane's absence, it was a senseless, self-inflicted wound.
THE FERDINAND FACTOR
The eight-month ban on Rio Ferdinand for missing a mandatory drugs test has knocked a huge hole in United's rearguard.
But the suspicion remains that if United had acted with just a tinge of humility and accepted a measure of wrong-doing instead of defending the indefensible, the punishment might have been less severe and damage limited.
Tactically and morally wrong - and a serious error.
THE JANUARY TRANSFER WINDOW
Ferguson's failure to fill the gap left by Ferdinand's absence looks more like a major blunder with every passing week
United have not kept a clean sheet for nine matches and have recorded only three in their last 18 games.
Ferdinand gap has not been filled
Ferguson set his stall out for Louis Saha as a Champions League foil for Ruud van Nistelrooy up front.
All very well, but it smacked of putting a new roof on when the foundations were in serious need of repair.
Ferguson's decision not to sign a top-class central defender as cover is inexplicable. Middlesbrough's Gareth Southgate could surely have been lured to Old Trafford - or, if not, a supposed worldwide web of contacts could have produced talent.
ROCK OF GIBRALTAR
Ferguson says his ability to manage Manchester United was not affected by the row over breeding rights for Rock of Gibraltar with racing tycoon and major United shareholder John Magnier.
This may be so, but it provided a grim backdrop to United's season, with questions about the club's transfer dealings and threats of the courtroom.
The dispute has been settled - but the outbreak of peace will not be celebrated by an appearance in the Champions League final.
United have been hit by several shots across the bows from the mighty financial power of Chelsea owner Roman Abramovich.
He lured respected chief executive Peter Kenyon away from Old Trafford and has muscled in on transfer territory traditionally dominated by Ferguson.
United coveted Blackburn's Damien Duff for years, but had no answer to Chelsea's £17m summer bid.
Abramovich is haunting Old Trafford
And despite appearing to have a deal for PSV Eindhoven's Arjen Robben tied up, Chelsea blew them out of the water again when the Old Trafford paymasters reduced their offer.
Ferguson insisted they would not have matched Chelsea's offer - but it was a symbolic defeat for the one-time master of the transfer market.
One defeat - no matter how damaging - will not bring the institution of Manchester United crashing down just yet.
Ferguson has suffered blows before, but few as potentially significant as this.
The summer will be crucial for Ferguson. The guard must be changed. Top-class proven talent must be brought in - even if it means battling Abramovich's chequebook.
It may not be the end of an era yet, but it is certainly Ferguson's most testing time.