Two goals from Mikel Rico, one in each half, saw a superior Athletic progress after a 1-0 defeat in the first leg a week ago and maintains the Basques unbeaten in their new San Mames Stadium.
Espanyol and Alcorcon produced a thrilling tie in which two goals in a five minute spell at the end of the game saw Espanyol qualify to play Real Madrid after it looked as if they would crash out to their second division rivals.
Alcorcon travelled to Barcelona on the back of a 1-0 win last week and when Oscar Plano put them ahead on Wednesday that needed Espanyol needing to score three times in order to qualify.
Simao Sabrosa and Sergio Garcia leveled the tie before the midway point of the first half, but needing to score again as a result of the away goals rule Espanyol wasted a host of chances and when Javito netted for Alcorcon with 10 minutes remaining, some home fans even began to leave their ground.
That proved to be a bad decision as first Victor Sanchez and then Pizzi scored excellent goals to turn the jeers to cheers take Espanyol into the last eight.
