Making a strong start, North Otago applied the early pressure and early tries to lock Charles Elton, wing Adam Johnson and wing Howard Packman left Wanganui playing catchup for the remainder of the game.
Two key contributors to the wings' tries were centre Lemi Masoe who latched onto a kicked ball to race down the sideline to set up the chance inside while another kick to fullback Patrick Pati allowed him to show his skills in slipping the defence and sending Packman in.
Just when they seemed to have done enough to get within touching distance, North Otago scored again and with halfback Robbie Smith, one of the tryscorers, landing two penalty goals, the issue was put beyond Wanganui.
Dominating possession and putting pressure on Wanganui to force mistakes, North Otago won the trophy for the third time, and for the first time since 2010. Wanganui last held the Cup in 2017, having completed a hat-trick of wins.
North Otago captain and prop Ralph Darling, who landed a stupendous dropped goal just before halftime, said the team had benefited from having an early season Ranfurly Shield challenge against Otago.
That brought the side together earlier than usual and they set the goal to make the final from that early stage.
"Wanganui have been an outstanding side every year, no matter who the personnel are in their team.
"We knew we needed to start well. Being a tight bunch of boys that paid dividends with the result we got today," he told SKY Sport.
The dropped goal had come about because he had just been standing off a ruck having a bit of a rest and he ended up with the ball and just shut his eyes and hoped for the best.
North Otago coach Jason Forrest paid credit to his players saying they had made it easy for the coaches.
"We knew we had to front up physically and go through middle before opening up when we earned the right to go wide," he said.
The team had been a tight group under usual captain Sam Sturgess, who wasn't able to play in the final, and Darling, his deputy.
So far as his captain's dropped goal was concerned he said: "That's Ralph, he plays off the cuff. He's an amazing player."
Wanganui coach Jason Caskey said the better team won on the day. Wanganui had worked very hard to make the final after a disappointing start to their campaign but it had proved a step too far.
"We couldn't do a lot of things we wanted to do today and that was down to North Otago not letting us," he said.
Tackling had not been as efficient as they would have liked and they weren't able to get the ball out into the wider channels that were so effective when they beat Wanganui a month ago during round robin play.
Scorers: North Otago 33 (Charles Elton, Robbie Smith, Howard Packman, Adam Johnson tries; Smith 2 con, 2 pen; Ralph Darling dropped goal) Wanganui 19 (Angus Middleton, Lindsay Horrocks, Vereniki Tikoisolomone tries; Nick Harding 2 con).