Sertić traveled back to Croatia when Independent State of Croatia (NDH) was established during the April war. Sertić was appointed by Ante Pavelić for Commander of all Ustaše Military Units on 3 May 1941. At the same time, he was appointed as the commander of the 1st Ustaše Regiment. After two weeks he was dismissed from this position following quarrels with Slavko Kvaternik and other high-ranking Ustaše officials. His conflict with so-called Rasovi continued through the whole war.