The Wellington Firebirds will host Auckland in Friday's preliminary Twenty20 final after the Aces beat the Central Districts Stags by six wickets in a must-win match at Eden Park.
The Lou Vincent inspired win lifted Auckland into third place after the 10th and final round, equal with Northern Districts on 20 points but ahead on run rate.
Second-placed Wellington have hosting rights at the Basin Reserve with the winner advancing to play top qualifiers Otago in the final at Dunedin's University Oval on Sunday.
The New Zealand champion then advances to the qualifying tournament for the lucrative Champions League.
Tonight's game was reduced to 18 overs because of rain and Central posted 132-7 batting first, with Auckland's target then revised to 136.
Auckland chased that down with an over to spare as former Black Caps opener Vincent paced the innings with an unbeaten 52 from 39 balls.
He received valuable support from Donovan Grobbelaar, who clubbed an unbeaten 36 from 19 balls.
For Central, opener Mathew Sinclair top-scored with 44 from 40 balls, with Carl Cachopa's 15-ball 25 the next best effort.