Wanganui set their sights on tackling King Country at their strong points - the scrum and midfield - and it worked a treat as they secured their place in next year's NPC second division.
Having finished fourth in the third division round-robin, they beat top finishers South Canterbury the previous weekend to make the final.
Wanganui won 28-16, outscoring the home side three tries to two.
Coach Milton Haig said his side had targeted King Country's strength in the scrum and midfield. "We wanted to play the game at the right end of the paddock. I'm really pleased with the work-rate from the forwards. The scrum went better as the game went on.
"The guys were unbelievable; they put their bodies on the line. It was the most committed display this season.
The victory capped off a stunning mid-season recovery from Wanganui.
King Country coach Graeme Crossman was left to bemoan lost opportunities.
"We just didn't have any ball to work with in the first spell. We were stumbling around in our own half on defence. We made ground when we had the ball, but we were not accurate enough."
Wanganui fullback Darren Firmin opened the scoring with a penalty in the sixth minute and increased the lead to 10-0 when he converted Rauhina's try after the forwards had driven 50m.
King Country's first-five Michael Blank closed the margin to 10-3 with a penalty goal, but Firmin kicked a second penalty to regain the 10-point margin after 25 minutes.
King Country brought play deep inside Wanganui's 22. No 8 Josh Ostern crashed ahead and the ball was moved wide for wing Robbie Burgess to score.
From the kick-off Wanganui replied with a try to winger Che Barlow.
Blank kicked a second penalty in the 40th minute to go to the break with Wanganui ahead 18-11.
King Country started the second half strongly and looked to be gaining ascendency, but errors undid their good work.
In a decisive moment, Wanganui halfback Josh Edwards broke from a ruck to feed centre Areta Lama and regather the pass to run 20m to score.
Firmin added the conversion for Wanganui and kicked a third penalty 10 minutes from time to put the game beyond King Country's reach at 28-11.
King Country threw everything at Wanganui in the last 10 minutes and were rewarded with a try to replacement winger Marc Baggott.
NPC points table