At Auckland's Keith Hay Park, Three Kings United trailed 0-1 at halftime but came through with two second half goals to upset Wellington's former holders Miramar Rangers 2-1.
At Newtown Park in Wellington, Olympic scored a goal in each half to hand two-time winners Manurewa a 2-0 defeat in their semifinal.
Sam Matthews sealed the win for Three Kings with a powerful volley from 22 metres in the 78th minute.
Three-times Cup winners Miramar had the measure of Three Kings in the first half, with All Whites midfielder Andy Barron unlocking the Aucklanders' defence for Dominic Rowe to fire the visitors into a 17th-minute lead.
Each side had strong penalty claims turned down by referee Peter O'Leary, but Three Kings goalkeeper Greg Walters had a major role in preventing Miramar from extending their lead.
But by the time Stu Hogg lashed an 55th minute equaliser into the roof of the net from close range, Three Kings were matching their more storied opposition.
Matthews' stunning winner then booked them a maiden final appearance.
Olympic proved too good for two-time Cup winners Manurewa, with Mickey Malivuk tapping in after half an hour and Jimmy Haidakis expertly curling a 57th minute freekick around the defensive wall from 30 metres out.
The final is scheduled to be played on either September 19 or 20 most lilely at North Harbour Stadium.
