Smith (38) started the final round five shots off the pace but made birdies on the first and sixth holes.
He had a golden start to the back nine, birdieing 10, 11, 13 and 14 and finished his bogeyless round with four solid pars.
Smith finished nine shots clear of Caallum Judkins (Wakatipu Junior) and Michael Ormandy (Otago), who tied for second.
It was a changing of the guard at this year’s tournament as Brent McEwan had previously dominated the event, winning in 2005 and claiming the past nine titles.
Scoring was not as low as expected as several players found difficulty adapting to the hard and fast greens after one of the wettest starts to this year’s trial series.
Smith shot a 4-under 68 in the first round to take a four-shot lead over Ormandy and Judkins with local hope Stephen Waby two further shots back.
Smith dropped a shot at the par-4 third hole but birdied the eighth and ninth holes to turn 1-under.
He had a faultless run coming home with six pars and birdies on the 12th, 16th and 17th holes.
He started his afternoon round at the 10th with four pars but then the wheels fell off starting with a triple-bogey 7 seven at the 14th.
He then bogeyed 16 and doubled 17 to turn 6-over-par before carding two bogeys coming home for a forgettable 81.
This placed him three shots off the pace with Ormandy and Waby sharing the lead on 2-over 146.
Fresh from his fifth place at the national under-19 event, Judkins posted two solid rounds to be one shot behind the overnight leaders.
But it was Judkins who set the pace yesterday morning with the lowest score to date of 67 to take a three-shot lead after the third round.
Starting at the 10th he started his faultless round with birdies at the 15th and 16th holes turning 2-under.
Coming home, he birdied the third, fifth and sixth holes along with six pars for his 5-under-par round.
This gave him a three-shot lead over Ormandy while Smith was back on track with a 2-under 70 which included an eagle two on the testing third hole.
This put him five shots behind Judkins while McEwan and Waby looked out of contention two further shots back.
Ormandy carded 77 in the final round while Judkins faded back with his highest score of 80 to finish.
