For the 2003–04 season, Brøndby bought goalkeeper Karim Zaza who became their first choice, leaving Ankergren to spend the season as back-up keeper, playing only one match. At the start of the 2004–05 season, Zaza suffered an injury and Ankergren played the entire season as Brøndby's starting goalkeeper, even after Zaza had recovered. Ankergren finished the season setting a league record 18 clean sheets in 32 matches, and helped Brøndby win the Double of both the 2004–05 Superliga and 2005 Danish Cup titles.