On the Trump International Golf Links in Aberdeenshire, 42-year-old Jamieson proved a surprise victor by two shots on Sunday, after a five-under 67 shot him to an 11-under-par total.
The world No.465 had last won on the European tour in 2012 when he lifted the Nelson Mandela Championship in South Africa, and had to admit: "Fourteen years, that's wild! It's just so tough, so hard to win.
"I was so patient all day ... just can't believe I've won."
Jamieson prevailed ahead of England's Matthew Jordan, who shot a 70, and Andy Sullivan (68), who was two strokes further back in third place.
Overnight leader Shaun Norris, who'd holed for an albatross two on Saturday, slumped with a last-round 76 and ended up having to settle for joint seventh.
Just as for Jamieson, it was a big day for the 24-year-old Scottish-born West Australian McKinney, the world No.741 who enjoyed the best European tour result of his career, finishing tied for 10th after a final-round 71 left him at four under.
The highlight of his final round, after he'd double-bogeyed the ninth and bogeyed the 10th, was to hole out for a spectacular eagle two from 143 yards at the par-four 11th.
Self-described as a "Scossie", born in Kirkcaldy, Fife, McKinney moved with his family to Australia when he was 13, where he carved out an excellent amateur career.
He often seems to impress when he returns to Scotland, and four years ago won both the Australian Amateur and the St Andrews Links Trophy in his final year as an amateur.
