Dave Woods, commentating on Channel 5 got it spot on: Old Trafford, he said, used to be a fortress on European nights, now it has become a gift shop. For the third time this season, Manchester United were embarrassed at home in Europe.
And the trio doing the damage to them have not come from the continental elite. It is not Real Madrid, Barcelona or Bayern giving Alex Ferguson's team the runaround while their fans out-sing the locals in the stands. It has been Basel, Ajax and last night the quite excellent Athletic Club.
How did this happen? How did a club that has been in three of the last five Champions League finals suddenly transform into a flake? How were they quite so comprehensively taken to Basque?
The theories were spinning round last night. One suggests that Old Trafford is about as close to a cauldron these days as Nick Clegg is to popular. The regulars, sated on success, are simply no longer as excited by European nights as they were in the days when Maradona turned up wearing shorts so tight they constituted a restraining order, or when the great Juventus team turned up in the mid 90s, or when the Brazilian Ronaldo was given a standing ovation nearly a decade ago, so therefore don't make anything like a scary noise. It is a legitimate line of thought. Trotting out at Old Trafford these days, visiting teams are not so much welcomed to hell as to a vicarage tea party, where an atmosphere of polite silence obtains, broken only by the occasional clink of crockery from the posh seats.
But then again, in common with the Emirates and Stamford Bridge, it has been like that for a while. The crowd's involvement in big European nights has, for a good decade, been one of observation not participation.
In any case, petrifying the opposition should not be a requirement for a side as accomplished as Ferguson's to prosper. Nor can it be said the manager is fielding weakened line-ups. There may have been some complacency in his selection against Crystal Palace in the League Cup - another home knock-out humiliation this term - but last night Ferguson sent out a proper eleven.
Sure, there may have been one or two absentees you might expect to see back in the fold for a Premier League game, principally Paul Scholes and Rio Ferdinand. But this wasn't the stiffs being taken apart. Though frankly the way he defended - or rather failed to defend - for Athletic's third goal, Rafael looked not so much stiff as prematurely arthritic.
And this was surely the issue at the heart of the decline: United's defending has been woeful in Europe this season. Their back line has looked horribly unsure when faced with quick, incisive passing of the sort Athletic engaged in all night. As demonstrated in that third goal, they have looked particularly vulnerable to the breakaway. Which is generally the major attacking tool used by the visiting team in Europe. Time and again United have been caught high up the pitch by sudden counters. Last night David De Gea saved them from total embarrassment, his effort maintaining the possibility - albeit a faint one - of progress in the Europa.
It is an odd one, this, as United have long been masters of the breakaway themselves. Particularly in Europe. Remember the way they destroyed Arsenal in the 2009 semi-final? You would have thought, since they know how to do it, they should know how to stop it.
One of their problems is - since the long demise of Owen Hargreaves - they don't have a proper holding midfielder. Phil Jones was picked there last night for precisely that purpose, to shield the back four, to be a first line of defence in the event of breakaway. But he was pushed back into emergency cover in the centre of defence when Chris Smalling was injured.
Michael Carrick came on into his position, but Carrick is not that kind of midfielder. His best work is done in the opponents' half, between then centre circle and the edge of the area, maintaining possession, changing the angle of approach and picking out the killer pass. Not providing the covering tackle. And he hasn't the pace to chase back.
Moreover, when the opposition has breached the midfield barriers, they immediately discover that the back line isn't quite what it was a couple of years back. Jonny Evans improves with every game, but he and Smalling or Jones are no Ferdinand and Vidic. It is the Serbian's presence that is most missed. The organisation as much as the brute presence he brings is not easily replaceable.
But if this is the case, and United have suddenly found themselves this season vulnerable to the breakaway, how come they are not being similarly found out in the Premier League? They have lost but twice in the league at home all season, though intriguingly their most traumatic reverse was against a Manchester City side who caught them on the break half a dozen times.
It is partly because visiting teams in the league don't set themselves up on the counter as much as visiting teams in Europe. But you wonder, watching Athletic's energetic breaks last night, whether Premier League managers will be coming to Old Trafford for the rest of this season with designs on the breakaway.