McEwan (30) shot rounds of 66, 72, 68 and 74 for a total of 280 to win by an impressive nine-shot margin from Invercargill's Tyler McLean. Liam Balneaves (Greenacres), Nick Borren (Otago) and Simon Hollyer (Wanaka) tied for third three further shots back.
It is difficult to match his 280 score with other championships as refurbishment of the par four 17th meant it was replaced by the par 3 Crossways hole, reducing the course par to 70.
Scoring was not easy during the weekend as the capacity field was plagued by gusty winds.
McEwan's low darting shots helped him keep the ball in play throughout the event while many other senior golfers drifted off target.
"I played for position all weekend and was very pleased with that aspect of my game," McEwan said.
Chisholm Park golfers won the next two grades with Masters (over-40) golfer Kyle Geary winning the Senior B title by five shots from Daniel Elder (Otago).
Intermediate honours went to the club's junior, Conor Jamison, with a convincing 15-shot winning margin.
Former Otago representative Chris Idour (St Clair) shot 76 and 78 to win the Masters (over-40) title which was played over 36 holes.
But it was McEwan who set the pace with three birdies on the first three holes on Saturday morning.
His only blemish in an almost faultless round of 66 was a three putt on the fourth green but he followed this with birdies on the 10th and 13th holes.
This gave him a four-shot lead over McLean and Hollyer after the first round.
A two-over-par 72 in the afternoon cut his lead to two with McLean in second place, while Hollyer was one further shot back.
But McEwan increased his lead to eight with a 68 yesterday morning with Hollyer second and McLean 10 shots off the pace.
McLean made an early charge in the final round but McEwan stuck close to par, giving the chasers little chance of closing the gap.
A tired finish, dropping shots at the 14th, 15th and 16th holes, took a little gloss off his final round but par 280 for four rounds in tough conditions was most satisfying for Otago's No. 1.
