Born in Split, SR Croatia, then still part of Yugoslavia, Vastić started to play for local club Jugovinil (today GOŠK Adriachem), before joining RNK Split at time playing in Yugoslav third level.
He left Sturm for a one-season spell with Japanese club Nagoya Grampus Eight, after which he returned to Austria to spend two seasons with Austria Vienna before joining LASK Linz in the summer of 2005.