Forrest, who lifted his maiden European Tour title at St Andrews almost exactly four years ago, took control of windy conditions over the weekend but saw his three-shot overnight advantage trimmed to two after Todd Clements’ birdie on the opening hole.
However, when Forrest birdied the fourth and Clements carded a triple-bogey eight at the same hole, the Scot led by five and never looked back.
The world number 294, who double-bogeyed the last, added two more birdies and a dropped shot in a closing 72 to finish with an eight-under-par total.
“It’s amazing, just speechless,” Forrest said. “I think it is the same week as I won four years ago on the calendar so just amazing, that must say something about this week and being at home.
“I just can’t believe it. It’s been such a tough year on the golf course. It’s just a crazy game that you can go and come out and do this, with what feels out of nowhere.
“It’s just that old chestnut that one week can turn things around and it has.”