North Harbour led 33-19 at half time.
North Harbour scored 10 tries to five, only one of them by a forward, captain and hooker James Parsons, while it was their first win over Taranaki since 2007.
The top qualifiers opted to rest their most experienced players while North Harbour were at near full-strength.
The Harbour winger Tevita Li scored five tries.
The Premiership play-off picture had already been finalised for next weekend, with top seeds Taranaki to host Tasman and Canterbury to host North Harbour.