 In 2002, aged 18, Iturriaga joined Athletic Bilbao following in the footsteps of his brother Iñigo, and meeting the criteria of the club's philosophy despite his birthplace by having developed as a footballer in the Basque region.He first appeared for the farm team, CD Basconia followed by the reserves, spending two seasons playing regularly with each squad.Iturriaga was definitely promoted to the main squad for the 2006–07 campaign, but only appeared in four La Liga games as the side finished one place above relegation (17th).