Otago batsmen Jacob Duffy (left) and Michael Rippon. Photo: Getty Images
The Volts managed to rack up 283-7 and then restrict the Aces to 280-7.
It was a team effort all round from Otago, with Neil Broom's 50 the top score.
Quick runs from Anaru Kitchen, Josh Finnie and Christi Viljoen toward the death helped Otago post a score that proved too much for the Aucklanders, just.
Youngster Nathan Smith was the pick of Otago's bowlers, finishing with figures of 2-44 from his 10 overs.
The final will take place on December 1 at University of Otago Oval.
See the full scorecard here.
