Brilliant Bilbao too good for United
Already trailing 3-2 from the first leg, United were effectively out of the competition when Fernando Llorente scored a brilliant opener for Bilbao.
Oscar de Marcos netted a second after the break, although at least Rooney limited the damage 10 minutes from time.
United survived a major scare when Llorente found Iker Muniain with a superb pass. Muniain's shot struck the base of a post with David de Gea beaten and De Marcos drove the rebound wildly over when he should have scored.
De Marcos had another shot saved before Athletic took the lead in magnificent style. Fernando Amorebieta launched a long ball across the pitch from halfway. There appeared little danger, even as the ball dropped over Rio Ferdinand's shoulder - but Llorente met it with a first-time volley, that gave De Gea no chance as it flew into the opposite corner.
It was the least Athletic deserved after proving their Old Trafford triumph was no fluke and meant United had to score at least three times to go through, something they did not appear capable of. Ryan Giggs' corner was easily collected by Gorka Iraizoz on a rare United foray forward.
When De Marcos and Markel Susaeta combined to set up Andoni Iraola early in the second half, the visitors almost conceded another memorable goal. Instead of shooting, the full-back weaved his way past three defenders inside the United box. It was brilliant stuff but the Athletic skipper spoiled his hard work by flicking the ball narrowly wide.
Rafael was booked for deliberately handling an attempted pass by Herrera, before Chris Smalling - in a Petr Cech style helmet to protect a head wound - and Paul Pogba, on his 19th birthday, were introduced after 63 minutes for Rio Ferdinand and Michael Carrick. It was the clearest evidence that Sir Alex Ferguson had given the tie up.
When De Marcos netted Athletic's second from Iraola's cross two minutes later, it was. Pogba was booked for a late challenge on Herrera and, having elected to leave Rooney on, hearts were in mouths when he took his time getting up from a tangle with Jon Aurtenetxe.
Thankfully he got to his feet and 10 minutes from time curled home a brilliant effort of his own - but it was far too late for United.
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