The Ayrshireman’s stunning six-under-par closing effort at the Aberdeenshire venue secured a one-shot win from overnight leader Jonathan Caldwell in the final regular event of the season the third-tier circuit.
He secured a £10,000 top prize after finishing with a 16-under-par 200 total, making it a hat-trick of tartan triumphs this season following earlier successes by Daniel Young and James Ross.
“I played great right through today, so I knew I just had to keep it going,” said McDonald, a former Scottish Boys’ Stroke-Play champion and winning Walker Cup team member at Royal Lytham in 2015.
“It feels amazing. The professional game is definitely different from the amateur game and I am just delighted to get the win. I am just going to enjoy it.”
The success lifted him to 13th in the Order or Merit heading into the season-ending Tour Chanmpionship at Desert Springs in Spain, where five Challenge Tour cards will be up for grabs.
“One box was ticked when I made the cut,” he said of securing his spot in the three-round event at the end of October. “All I was thinking today as I had nothing to lose and I was just aggressive and I am glad it paid off.”
A last-day 70 left Caldwell having to settle for second, with Braid Hills-attached Paul McKechnie finishing a shot further back in third place following a closing 67 that contained six birdies.