 In the 1965–66 season, Celje finally became the Slovenian republic first league champions, and after successful qualifications one season later in Slavonski Brod, finally became members of the elite Yugoslav Handball Championship.The maiden season in the first Yugoslavian league wasn't so successful, as Celje was relegated back to the republic league (the Slovenian First Republican league was basically the Yugoslavian second division), but managed to come back to the first league the following season.Jure Koren was the first Celje player who was drafted in the Yugoslavian national team.