The Red and Blacks trailed 15-5 at half-time, before levelling the scores with a penalty goal and converted try to Braydon Ennor.
The two teams then played out 20 minutes of overtime, with Canterbury fullback Chay Fihaki breaking the deadlock with a decisive try.
The win means Canterbury host Hawke's Bay in their semi-final, with Otago to entertain Bay of Plenty.
NPC COVERAGE WITH NZ SAFETY BLACKWOODS. TAKING CARE OF BUSINESS.