By Ian Herbert
The end of an unhappy affair, which felt very much like Manchester United being put out of their misery, frees them to repulse Manchester City's title quest. But the gulf in class in both legs of this fixture has left the impression of a club deep in transition.
Gary Neville has written of his difficult early years in Europe with United, learning how unforgiving of errors Europe can be. Tom Cleverley, Chris Smalling, Phil Jones and Rafael da Silva will concur with that sentiment, though Sir Alex Ferguson - determined to build up one last group of young players before he goes - said this was a proving ground.
"I don't think we can complain about the result," said the United manager. "We try to analyse this season against other seasons. It's a bit difficult. I think there is a root [cause] in terms of some of those goals we have lost in these tournaments – they have been pretty poor, so its something we need to analyse, that."
Of the night's many bad moments for Ferguson, the sight of Andoni Iraola sashaying past three of his players eight minutes into the second half was perhaps the most punishing. Iraola's subsequent miss was almost beside the point. Ferguson's acknowledgement that it was time to look towards Wolves on Sunday came just past the hour when he introduced Smalling and then Paul Pogba. Within minutes, Smalling's defensive header had been seized upon by Oscar de Marcos and the ball smashed home. Pogba was booked inside 10 minutes.
Athletic's intensity panicked United, who needed a spark of invention. None ever looked likely from a midfield expanded to five men. After 13 minutes the tie should have been put out of reach when Fernando Llorente steered the ball to Iker Muniain. He smacked a low shot against the right post and De Marcos fired the rebound over.
Bielsa's side's first goal was exquisite, served up by a 40-yard cross-field ball from Fernando Amorebieta, which was tracked by Llorente as it fell over Rio Ferdinand's shoulder. The striker volleyed home.
Wayne Rooney did not even muster a smile when he punched in United's consolation goal from 20 yards out, 10 minutes before time.
"What we have seen tonight... is a team whose work-rate is higher than anyone else I have seen in Europe and that takes you a long way," Ferguson said of Bilbao.
Their red and white carnival lasted deep into the night.