The 27-year-old Australian birdied the last three holes at Glen Abbey to triumph by one over American Bubba Watson and by two over Canadian David Hearn, the 54-hole leader.
Day ended the tournament in style by rolling in a clutch 22-foot putt at the par-five 18th for a closing four-under-par 68 and a winning total of 17-under 271.
It was his second PGA Tour win of the season, the fourth of his career and followed up a strong tie for fourth at last week’s British Open.
Watson and Hearn, playing in the final pairing, shot 69 and 72, respectively. Hearn held a one-stroke lead standing on the 16th tee but Day and Watson, who made birdie on five of his six closing holes, both charged past him with blazing finishes.
Last Monday, Day’s birdie try on the 72nd hole at St. Andrews came up short and left him one shot shy of a British Open playoff won by Zach Johnson.
“To come off what happened last week and to be able to get the putt to the hole this time and come out as a winner, it just feels fantastic,” said Day, who let out a yell and fist-pumped as his last putt dropped.
Watson appeared to be out of the mix after a bogey at the 10th, before his birdie spree. Day was playing in the group in front of Hearn and Watson, and had to watch Watson’s short chip attempt for eagle slide by at 18 to know he had won.
“I’ve been putting in a lot of work, not only with my golf game, but with my body as well,” Day said. “Mentally, I feel like I was in the right spot coming into this week and I played fantastic.”
Hearn, vying to become the first Canadian winner at this event since Pat Fletcher in 1954, opened with back-to-back birdies, but stalled on the back nine.
“I’m real proud of the way I played and I’m really proud to be Canadian today,” Hearn said. “It was a pretty special day with all of the fans and the support that I had from beginning to finish.”