Koh then went back-to-back birdies for 13th and 14th to move to a one-shot lead. Geary on the 15th then grabbed the lead back and the crowd atmosphere was electric with three holes to play.
The clubhouse was a buzz with excitement as the lead changed back and forth.
In the end it was the persistent Koh, who put together a birdie, birdie, eagle sequence on the last three holes, who got his hands on the 100-year-old NZPGA Championship Trophy.
It is Koh's first NZPGA Championship and has capped off a brilliant summer for him.
"It's a bit of a blur, the entire day to be honest,'' Koh said.
''It was probably the best round of my career, I'm super stoked. It's such a prestigious event, I'm just thrilled.
Koh's putting was on point in his final round and when asked if he was going to frame his putter or keep it in his bag Koh said: "I was actually going to change it up, but I think I'm going to keep it in the bag now.
''My putter was just rolling amazing. The course was amazing, and I just want to take the chance to thank Te Puke Golf Club and the team for an amazing week."
Momoka Kobori had another solid day and finished with 9 under as the leading female in the field for a share of 11th for the championship in her first year as a professional.
The 2021 NZPGA Championship also found its first ever Regional Teams Championship winner.
The regional teams event was designed to engage golfing communities and enable them to come together to celebrate golf, the love of the game and where it started for players.
With Fox and Koh dominating, Auckland took the Rohe Trophy in strong fashion.
Team captain Koh was proud to be the first winning skipper.
"This has been a really nice touch to the tournament for us as players, it's been awesome for us all to reflect back where it all began as golfers and also those who are or have supported us in the shared love of the game. I'm really proud to be leading Auckland to win the first one."
PGA NZ general manager Dominic Sainsbury commended the golfing communities around New Zealand for coming together to make this the occasion that it was and highlighted the atmosphere the local Te Puke and Bay of Plenty community brought to the week.
"Sharing our golfing stories, where it all began for us and just soaking up the performance of professional golf and it being beyond just playing golf, Te Puke locals and the club have shown us what it really means, and we are really proud of how everyone in golf in New Zealand has pulled together to mark this as a real special occasion for PGA and golf in the country," Sainsbury said.
