Two brilliant individual tries by Wayne Gibson late in the first half made the difference when Harbour downed Dunedin at Kettle Park.
Dunedin was leading 7-3 when the second five-eighth worked his magic by scoring tries after 32 and 37 minutes to give Harbour a 13-7 lead at the break.
The first try illustrated the skills of Gibson.
He was quick on his feet and pushed off four tackles when he ran diagonally across the field before straightening up to score the try.
The midfield combination of Gibson and Siaosi Folau always looked dangerous with the ball in hand and it was only solid defence by Dunedin second five-eighth Michael Walding that kept the score respectable.
Dunedin came back into contention with an early try by wing Tumua Ioane to reduce the gap to one point.
But four penalty goals and a try by winger Craig Sneddon sealed the game for Harbour.
His covering work was sound and his speed tested the defence.
Pieter van der Merwe had a solid game at prop for Harbour and the best Dunedin forwards were prop Keith Cameron and flanker Tim Fraser.
Harbour 27 (Wayne Gibson 2, Craig Sneddon tries; Sneddon 4 penalty goals), Dunedin 17 (Tumua Ioane, Tim Fraser, Daryl Caldwell tries; Robbie Smith conversion).
Halftime: Harbour 13-7.
Referee: Jeff Grubb.
