[8] On 7 August 2007, Iraizoz signed for Athletic Bilbao for €4.6 million, returning to the club he spent one-and-a-half seasons with,[15] this time as the undisputed starter.

[16] However, due to a severe injury, he was left out of the squad for the second part of the campaign,[17] and his place (and shirt number) was taken by 37-year-old Armando, signed from Cádiz CF until June 2008.

[18] On 16 January 2010, his Player of the match performance helped the team hold on to its early home lead against Real Madrid, constantly denying Kaká and Cristiano Ronaldo's efforts.

[19][20] Additionally, he was in goal during the 2009[21] and 2012 finals[22] of the Copa del Rey lost to FC Barcelona,[23] and also helped defeat that opponent 5–1 on aggregate in the 2015 Supercopa de España for his only accolade at the San Mamés Stadium.

[24][25] In the opening match of 2014–15, at Málaga CF, Iraizoz appeared to score a last-minute equaliser with a header, but the goal was disallowed, apparently incorrectly.