Manchester United's Europa League challenge is hanging by a thread after Athletic Bilbao outclassed their opponents to claim a 3-2 victory in the first leg at Old Trafford.
Bilbao produced a sumptuous performance in the first instalment of the last-16 tie to leave United wondering how they will head to San Mames next week trailing by only one goal.
Wayne Rooney had given the hosts a first-half lead before converting an injury-time penalty to give the Premier League title hopefuls a glimmer of hope going into the return meeting.
United took the lead midway through the first half when Rooney pounced on the loose ball from close range after Bilbao keeper Gorka Iraizoz could only push out Javier Hernandez's shot.
However, the visitors were a constant threat and, after Markel Susaeta had lifted a good opportunity wide, Fernando Llorente deservedly header Bilbao level just before half-time.
Bilbao, who sit fifth in La Liga, were even more dominant after the break and United were indebted to David de Gea as the Spanish keeper denied twice denied Iker Munian either side of a brilliant stop from Llorente.
The Red Devils' flimsy defence, though, was eventually made to pay on 72 minutes when a wonderfully crafted move was finished by a crisp volley from De Marcos despite a suspicion of offside.
De Marcos was then involved in two late goals as first, his volley was pushed out by De Gea for Munian to crash home before his handball then gave Rooney the chance to pull a goal back from the penalty spot in stoppage-time.