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 departed Ajax in 2002 to join AZ, a mid-ranking club at that time. In his inaugural season, AZ ranked tenth in the Eredivisie, but circumstances improved when Co Adriaanse took over as manager in 2003. Under Adriaanse's leadership, AZ nearly secured European football in its first year.