Northern Districts needed 16 runs off the last two overs to overhaul Central Districts' total of 246 for six and book a home venue for the playoff game.
BJ Watling cracked an undefeated 113 but the home side stumbled, losing two wickets in the final over and fell five runs short.
Canterbury clinched home ground advantage with a five-wicket win against Otago in Timaru yesterday and will host Auckland in the preliminary final on Sunday.
Auckland had a comprehensive 67-run win against Wellington at the Basin Reserve.
Former Black Cap Lou Vincent smashed 112 off 116 deliveries to help his side post a formidable 320 for nine.
The winner of the Canterbury-Auckland game will gain direct entry to the final on February 13.
The loser will play the winner of the Otago-Northern Districts game for the right to play in the final.
Otago had a slim mathematical chance of finishing on top of the competition table before its round-robin match but was well-beaten by the form team of the competition.
Aorangi Park has been unkind to Otago.
Last year the fixture turned into a slug-fest with Canterbury posting a record score of 410 for five.
The Volts replied, whacking 371 for seven.
A total of 781 runs were scored for 12 wickets at an average of a shade more than 65.
Not a great day if you were a bowler.
But there was no repeat of that extraordinary game with Otago losing six wickets for 15 runs to be bowled out for a modest 220.
Otago had been coasting along, seemingly heading for a score of 250-plus.
Craig Cumming and Darren Broom were well set and starting to lift the tempo.
But Broom, having just brought up his third one-day 50, perished when he misjudged a quick single.
He hit the ball straight to Peter Fulton at mid off and could not beat the throw.
Broom's wicket triggered a dramatic collapse.
In-form wicketkeeper-batsman Derek de Boorder suffered the same fate as Broom - disappointingly run out after just one delivery.
Cumming's fine innings of 66 from 83 ended when he smacked a half volley into the covers and was caught by Michael Papps.
Papps offered Cumming hope when he juggled the ball but eventually completed the catch.
Opening bowler Mitchell Claydon did the rest.
He returned to mop up the tail, trapping Warren McSkimming in front and dismissing Nick Beard and Neil Wagner in his next over.
Claydon finished with four for 39 from 9.4 overs but, arguably, Rob Nicol was the pick of the bowlers.
The offspinner took three for 20 from 10 overs and was allowed to drift through over after over.
The batsman appeared unwilling to attack his bowling.
Otago made two early breakthroughs, removing the dangerous Nicol for five and Papps without scoring.
But Fulton reminded everybody he is still one of the best domestic batsmen in the country, anchoring his side's chase with 77 from 76 deliveries.
He found able support from Shanan Stewart (65) and experienced campaigner Andrew Ellis, who hit 55 from 45 deliveries to help seal the win.
The pair combined in an undefeated stand of 83 for the sixth wicket.
