With Rory McIlroy, Ian Poulter and Jason Day close behind, protecting a three-shot lead was seemingly going to be a tall task for Justin Thomas on Sunday at Firestone Country Club. Luckily for him, Thomas’ rivals made life much less stressful, with that trio shooting a combined 10-over par, allowing the leader to cruise to his first WGC victory and his third win this season, joining Bubba Watson and Dustin Johnson as the only three-time winners on tour this year.

That’s not to say Thomas didn’t play well en route to claiming the WGC-Bridgestone Invitational title. He did, smartly plodding his way around the golf course and firing a final-round 69 to win by four strokes at 15-under 265. He shot in the 60s all four rounds, figuring out a course that gave him fits in his first two tries, having tied for 28th a year ago and tying for 33rd in 2016. As the tournament gets set to move to Memphis in 2019, it’s not a bad send off for Thomas at Firestone.

“I’m glad I finally played well around here,” said Thomas, 25, who now has nine career victories on tour, seven of them coming in the past 18 months. “Just in time for it to leave, but yeah, got a little choked up when I saw grandma and grandpa over there.”

Thomas’ grandfather played in the 1960 US PGA Championship at Firestone, making the win all the more special.

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“It’s really cool,” Thomas said. “They don’t get to come out very often anymore. This is my first US PGA Tour win with them here, so that’s pretty cool.”

RELATED: The clubs Justin Thomas used to win at Firestone

The win comes after a shaky stretch by Thomas’ standards, including a missed cut at Carnoustie following a first-round 69. But it was clear he was getting close to his early-season form, this week confirming that fact, and it should give him plenty of confidence heading into the US PGA Championship at Bellerive, where he’ll be defending his title. A victory would make him the first player to win the event in back-to-back seasons since Tiger Woods in 2006 and 2007.

Finishing in solo second at 11-under 269 was Kyle Stanley, who carded a two-under 68 on Sunday. While he hasn’t won, Stanley continues to impress this season, finishing inside the top 5 three times and earning over $US3 million in prizemoney with this latest finish.

Dustin Johnson and Thorbjorn Olesen were the only players to apply any real pressure despite starting the final round 11 shots off of Thomas’ lead. Johnson went out in six-under 29, but cooled off on the back nine, making just one birdie and bogeying the 18th to finish with a six-under 64. He tied for third with Olesen, who also posted a final-round 64 that featured a back-nine 31.

Brooks Koepka’s three-under 67 earned him a solo fifth finish, his fourth inside the top five this year. Rory McIlroy, who stumbled to a three-over 73, was among a group that tied for sixth. Jason Day and Ian Poulter wound up in a tie for 10th with Si Woo Kim.