Iker Muniain struck moments after Athletic Club had been reduced to ten men as the Spanish side overturned a 2-1 first-leg deficit to edge past FC Lokomotiv Moskva on away goals.
After a fractious first hour, the game looked up for Marcelo Bielsa's men when Fernando Amorebieta received his second yellow card of the night after a lazy trip on Roman Shishkin. Yet within two minutes they were in front as Fernando Llorente headed Íñigo Pérez's corner towards the far post, where Muniain turned in. It was enough to earn a UEFA Europa League round of 16 date with Manchester United FC.
Athletic began the evening brightly, with right-back Andoni Iraola in particular given licence to get forward as the hosts sought to quickly swing the pendulum of this tie. Slick early skirmishes soon gave way to a battle of attrition as Lokomotiv dropped back en masse, a safety in numbers approach to combat the home side's pacy attack. The penalty areas became a conspicuous no-man's land.
The Spanish side sought a way through the visiting stronghold, but their long balls to striker Llorente scarcely made a dent. Subtlety and guile looked a more effective weapon, and on 32 minutes Gaizka Toquero, Ander Herrera and Iraola combined to eye-catching effect but the defender's final ball failed to find Llorente. Amorebieta's departure seemed to sound the death knell but amid the noise at San Mamés, Athletic did not hear it.
Herrera had a shot deflected just wide and from the resulting corner Muniain struck. Now the onus was on Lokomotiv, hitherto moribund as an attacking force save for one Felipe Caicedo effort on the cusp of half-time. Denis Glushakov finally forced Gorka Iraizoz into action with 20 minutes left, but that was as much as they could muster.