Zunic, the co-leader heading into the final round, held his nerve to finish at 21-under-par, shooting a 66 in the final round to win by a single shot.
Australian journeyman David Bransdon was second, and Kristopher Mueck was two shots further back in third place.
Young Wellington golfer Harry Bateman was the leading New Zealander at 14-under. Josh Geary finished at 12-under.