De Cler left Ajax in the summer of 2002 to join AZ, at the time a mid-table club. In his first season, AZ finished in the tenth position in the Eredivisie, however prospects changed when Co Adriaanse was appointed the side's manager in 2003. Under Adriaanse, AZ nearly secured European football in his first season.
De Cler left Ajax in 2002 to join AZ, a mid-table team at the time. In his debut season, AZ placed tenth in the Eredivisie. However, prospects brightened when Co Adriaanse was appointed manager in 2003. Under Adriaanse's guidance, AZ nearly qualified for European football in its inaugural campaign.