The 32-year-old is the fifth-straight Australian to win the tournament, and walks away with $180,000 for his trouble.
Griffin, who entered the day two shots behind overnight leader Hideto Tanihara, of Japan, went into the 18th hole a shot back.
But while he drilled his drive on the 433m par-4 hole down the middle, Tanihara's flayed right and into the rough.
Griffin then set up his winning putt with a lovely approach shot, while Tanihara could only find the bunker with his shot out of the rough.
The Japan golfer came within centimetres of saving par with a tough 5m putt, which would have forced a playoff, but he could not drain it.
That left Griffin to step up and sink the winner.
Griffin finished the day at 20-under-par, adding a final round 67 to his first four three rounds of 70, 65 and 65.
Kiwi Michael Hendry finished tied for third at 14-under-par.
Full story in tomorrow's Otago Daily Times.