The Blaugrana were heading for their fourth successive defeat in all competitions when Aduriz opened the scoring, but Pedro equalized before the Argentine took center stage again
After a wonderfully open first half in which both sides hit the crossbar, the visitors silenced Camp Nou five minutes after the break when Aritz Aduriz found the bottom corner of the Blaugrana net with a fine strike.
The Catalans appeared to be heading for their fourth successive defeat in all competitions, but Pedro turned home an Alexis Sanchez shot in the 72nd minute. Just moment later, Lionel Messi decided the game with a low free kick, thus moving Tata Martino's men back to within four points of Liga leader Atletico Madrid.
Martino acknowledged in the build-up that his debut season in Europe has not been satisfying after the club's Champions League and Copa del Rey challenges dissolved within the space of a week.
Things threatened to get even worse for Martino and Barca in the 11th minute, but Jose Manuel Pinto palmed Aduriz's shot around the post after Alex Song squandered possession in midfield.
That let-off seemed to spark Barca into life and Pedro went close four minutes later, but he could only hit a tame effort straight at Iraizoz following Messi's through ball.
The home side was lucky to stay level in the 31st minute, however. The in-form Aduriz saw a spectacular overhead kick come back off the crossbar, before Pinto smartly parried away Markel Susaeta's effort from the rebound.
Barca responded by hitting the crossbar itself almost immediately. Alexis Sanchez really should have done better following Adriano's low cross, but his shot from close range struck the bar.
Iraizoz was kept busy until the break, but parity remained and Athletic capitalized early on in the second period.
The unconvincing Marc Bartra surrendered possession to Aduriz on the edge of the area, and the Spaniard coolly slotted a precise shot into the bottom-right corner for his 16th Liga goal of the season.
Barca finally drew level in the 72nd minute as Pedro quickly shifted his feet to divert Sanchez’s wayward effort past Iraizoz after brilliant work from Dani Alves. Just a few moments later, the Blaugrana were in front.
Messi finally found his shooting boots from a free kick, placing an effort through the poorly-formed wall, and Iraizoz let it fly under him.
Messi and substitute Cristian Tello went close to adding a third late on, and Mikel Rico saw a last-gasp shot blocked away for the visitors.
Despite a late flurry, the champions held on to their slender win to close the gap on Atletico, while Athletic’s grip of the final Champions League place slipped ahead of next week’s showdown with Sevilla.