He finished two shots clear of former Queenstown golfer Jamie Anstiss, who scored 72 in the morning and, with the help of six birdies, finished strongly on 69 in the second round.
Daniel Barnett (Otago) was third on 142 while Kris Rush (Otago) carded 69 and 74 for fourth place.
Not all of the field found scoring easy but there were five sub-par rounds in the event.
Barnett set the early pace, turning 5-under on 30 for the front nine with birdies at two, four, six, seven and eight. With a birdie-3 on the 292m par-4 11th and another birdie on the par-5 14th, Barnett held a healthy lead at 7-under.
Despite a disastrous finish with three bogeys in the final four holes, Barnett was the lunchtime leader by one shot over McEwan. McEwan made five birdies in his morning 68 but dropped shots to par at the 11th and 18th holes.
Rush has been in a form trough in recent months but returned in style with a sub-par 69 to be third at lunch. McEwan's steady golf helped him home in the afternoon while Anstiss was the big mover, getting up to second. Barnett was in contention for gross honours tied with McEwan with four holes to play.
But in a repeat of his morning finish, Barnett dropped three shots on the final four holes to slide to third. The third trial will be over 36 holes at Wanaka next Saturday but many of the younger brigade will miss that event.
Wakatipu College will compete in the national intercollegiate at Coringa in Christchurch today while more than 20 Otago juniors will compete in the New Zealand under-19 championship at Harwood during the rest of the week. Next Saturday the Otago under-19 and under-16 teams will compete against Canterbury at Terrace Downs.
