Bilbao cruised to a 2-0 home win over the Nervionenses after two goals in the second half.
Neither of the two sides really managed to impress in the opening 45 minutes, with Bilbao getting the best chance to break the deadlock. Nevertheless, Fernando Llorente's fifth minute header was expertly saved by Javi Varas.
For Sevilla, Luis Fabiano tried his luck from long range, but the attacker's shot went harmlessly wide. Holding midfielder Ivan Rakitic also opted to test the goalkeeper, but his shot didn't worry Iraizoz too much.
The Basques somewhat fortunately opened the score halfway the second half. Sevilla defender Federico Fazio attempted to clear a cross from Koikili Lertxundi, but he deflected the ball past his own goalie instead to make it 1-0.
The guests then took over the initiative and Frederic Kanoute came close to restoring parity in the 75th minute. However, the Malian attacker was denied by Iraizoz. The Bilbao shot stopper pulled off another superb save only two minutes later when Kanoute got another chance.
Andoni Iraola eventually put the match to bed with two more minutes to go. The referee awarded Bilbao a spot kick after Julien Escude fouled Oscar de Marcos inside the area and Iraoloa did not fail from 12 yards.
Bilbao have climbed to fifth spot in the table following this weekend's results, while Sevilla have dropped to eighth spot. Athletic face an away game against Getafe next week, whereas Sevilla host table-toppers Barcelona on Sunday.