 Brought up in Athletic Bilbao's prolific youth ranks, Lezama, he made his senior debut in 1995–96, suffering Segunda División relegation with the B-team.In the following season, as Luis Fernández replaced Dragoslav Stepanović as manager, he was again deemed surplus to requirements and loaned, going on to experience one of his best years as a professional with neighbours SD Eibar in the same level.Released by Bilbao in the summer of 1997, Guerrero signed with Racing de Santander of La Liga, starting in most of the matches during the campaign and making his debut in the competition on 26 October in a 0–2 away loss against FC Barcelona, as the Cantabrians eventually retained their division status.