Vastic started his career with RNK Split although he was invited to play with Split's major club Hajduk. 1991, during the separation war in Croatia, he went to Vienna, where he played for First Vienna FC 1894 in the second division. The next two years he played for VSE St. Pölten, Admira Wacker in Austria and MSV Duisburg in Germany. 1994 he went to SK Sturm Graz where he stayed until 2002. This was the most successful time of his career. He became champion (2), won the cup(3) and the Supercup (3). He also played three times in the Champions League and reached in the season 2000/01 the second stage of the Champion League.