MacIntyre carded a final round of 68 at Hamilton Golf and Country Club to finish 16 under par, a shot ahead of home favourite Ben Griffin.
Griffin had piled on the pressure with birdies on the 15th, 16th and 17th to close within one of his playing partner, but could not find a fourth in a row on the last to potentially force a playoff.
That meant MacIntyre had the luxury of two-putting from 10 feet for the win, before embracing his father Dougie, who had been called on to caddie at short notice.
Asked why he was so emotional at the win, MacIntyre gestured to his dad as he told CBS: “Because of this … I’m speechless, to be honest. This is just everything for me, my family, my girlfriend, my team. I can’t believe I’ve done it with him on the bag.
Adam Scott was the best placed of the Aussies at the Canadian Open. (Photo: Getty Images)
“I’m crying with joy, but I’m laughing because I didn’t think it was possible.”
Adam Scott was the best-placed of the Aussies, finishing in a tie for 42nd after a final-round 69 left him at two under.
MacIntyre had seen his four-shot overnight lead wiped out in the space of four holes after he bogeyed the first and home favourite Mackenzie Hughes made a hat-trick of early birdies.
However, MacIntyre responded superbly to birdie the fourth, seventh and eighth to regain control of the $US7.4 million ($A11.1 million) event, despite having to ask for a drone which was being used for the television coverage to be moved on several occasions before he finally got his wish.
Another birdie on the 11th was followed by a wild tee shot on the 12th into a water hazard and another bogey on the 13th opened the door for the chasing pack, but the Ryder Cup star crucially birdied the 15th and safely parred the last three holes.
