Caversham and Roslyn-Wakari will play for the South Island title at Carisbrook this Saturday.
Nomads started better at the Caledonian ground than coach Steve Fleming's side, finding space where none should exist in the heart of Caversham's defence.
Gareth Rowe showed why he earned eight New Zealand caps and also played professionally in Singapore.
He drove play forward, where Jean Claude De Joux and Luke Petrie tested the home side.
It took just 12min before Rowe leapt high at a corner, headed across goal and De Joux nodded the ball in to give Nomads a 1-0 lead.
Minutes later, De Joux again found space enough to clip an intelligent lofted shot that beat keeper Liam Little and left the Caversham crossbar vibrating like a tuning fork.
Caversham swept up the field in reply, showing vintage passing skills, and from a long throw-in by Tom Jackson, Tim Cook bravely challenged and headed in a top-quality equaliser as keeper Jordan Buchanan tried to punch clear.
Six minutes later, Caversham fashioned a passing move that had Jeremy Wild switching play from the left to Croyden Wheeler.
His early centre was not cleared and Dave Dugdale pounced to shoot his side into a 2-1 lead.
Before half-time, Caversham had its best spell.
Jackson harried defenders into error, Cook laced an acrobatic volley, Darren Overton made a couple of dangerous runs and the industrious Robbie Deeley also hit shots.
After the break, Mike Smith demonstrated his versatility with a superb last-man tackle as Petrie shaped to shoot running into the box, then the Caversham captain showed his athleticism to get forward and hit what might be the goal of the season with a drive that hit the Nomads net before heads could turn.
At 3-1, Caversham was in total command.
First Wheeler headed against the post, then Cook, in acres of space, headed a great chance over the crossbar, and Overton also tested keeper Buchanan.
"We started poorly, but did well to fight back and dominate midfield," Fleming said.
"We broke up their attacks, made lots of interceptions, and won all the loose ball.
"It was a great effort, and that was some goal from Mike Smith."
In Nelson, Roslyn upset the form book by beating Suburbs with second-half goals from Anthony Hancock and Sean Brand.
Unbeaten Nelson's championship-winning record of most goals scored and fewest conceded was left in tatters by a concerted Roslyn team effort that had player-coach Terry Boylan beaming with delight.
"Everyone did their job, from big Pete [Evans] in goal all the way forward to Ant [Hancock] and Sean [Brand], plus the subs, Tim Dalman and Hannan Husten, when they came on," Boylan said.
"It's especially good that two Dunedin teams have emerged as South Island finalists, with not a Mainland team in sight."
