Erceg entered the senior ranks in 2003. She placed 112th in the all-around at the 2003 World Championships and did not qualify for the 2004 Olympics, but continued training. In 2004, she placed 14th in the all-around at the European Championships. Erceg won her first major international medal at the 2005 Maribor World Cup, where she placed second on floor exercise. At the 2006 Maribor World Cup, Erceg won two additional medals, a silver on the uneven bars and a bronze on vault.