Harper (20) beat Mark Brooks (Queenstown) on the final green to win his second major title in the Aorangi district.
In 2005, Harper coasted to a convincing win in the South Island under-19 event on the St Andrews course.
"I have a liking for these types of courses and this is the fifth time I have played in this event," Harper said.
Harper turned one-up on Brooks in the final but Brooks birdied the 10th to get back to square.
There was never much breeze between the players on the homeward nine and the pair went on to the final hole all square.
Brooks had a difficult lie in the rough on the final hole and his shot became even more difficult when Harper played his fine approach.
Brooks' ball finished well through the green and under a car which was moved to allow him to play.
Brooks' recovery ran well past the hole and finished on the apron.
He showed his determination by holing his chip for a par 4, forcing Harper to make his birdie to take the title.
Bo Houston (Ashburton) won the intermediate title while Ryan Cockburn beat top qualifier James Shaw to take the junior title in an all-Ashburton final.
