Canterbury required an extra 20 minutes to see off a gallant Taranaki outfit 51-27 and book their place in next week's ITM Cup final.
Locked at 27-all after 80 minutes at AMI Stadium on Saturday, the defending champions and their visitors headed into two ten-minute halves to determine who would make the final.
But the Amber and Blacks ran out of steam as Canterbury put the result beyond doubt with three tries in extra-time through Wyatt Crockett, George Whitelock and Jordan Taufua.
Canterbury full-back Tom Taylor contributed 17 points from the tee before fly-half Tyler Bleyendaal took over with 11 points kicked in extra time.
Earlier, a late try to Taranaki replacement Seta Tamanivalu levelled the scores after Canterbury had led throughout the match.
Taranaki pivot Beauden Barrett had the chance to win the match from the sideline, but his conversion was waved away.
Meanwhile, Otago and Counties Manukau will battle it out in the Championship final with the winner earning promotion to the Premiership.
Otago overcame an 18-31 deficit midway through the second half to beat Tasman 41-34 with Glenn Dickson contributing 21 points from the tee.
In the other semi-final, Counties Manukau dominated the second half as they overwhelmed Southland 48-23. The Steelers scored six tries to two - five in the second spell - to set up a date with Otago in Pukekohe next weekend.
Tries: Crockett 2, Todd, G Whitelock, Taufua
Cons: Taylor, Bleyendaal 3
Pens: Taylor 5, Bleyendaal
Tries: Marshall, Eaton, Walker, Tamanivalu
Cons: Barrett 2
Canterbury: 15 Tom Taylor, 14 Adam Whitelock, 13 Robbie Fruean, 12 Ryan Crotty, 11 Johnny McNicholl, 10 Tyler Bleyendaal, 9 Andy Elllis, 8 Luke Whitelock, 7 Jed Brown, 6 George Whitelock (c), 5 Dominic Bird, 4 Joel Everson, 3 Paea Fa'aunu, 2 Ben Funnell, 1 Wyatt Crockett.
Replacements: 16 Codie Taylor, 17 Joe Moody, 18 Matt Symons, 19 Jordan Taufua, 20 Willi Heinz, 21 Telusa Veainu, 22 Stephen Gee.
Taranaki: 15 James Marshall.14 Andre Taylor, 13 Kurt Baker,12 Jayden Hayward,11 Waisake Naholo,10 Beauden Barrett, 9 Chris Smylie, 8 Jarrad Hoeata, 7 Chris Walker, 6 James Broadhurst, 5 Jason Eaton (c), 4 Craig Clarke, 3 Michael Bent,2 Timo Tutavaha, 1 Chris King.
Replacements: 16 Laurence Corlett, 17 Carl Carmichael, 18 Nemia Soqeta, 19 Adrian Wyrill, 20 Jamison Gibson-Park, 21 Seta Tamanivalu, 22 Jackson Ormond.
Referee: Mike Fraser