LOS ANGELES - Justin Thomas, limbering up for his PGA Championship title defense, fired a one-under par 69 on Sunday to win the WGC Bridgestone Invitational by four strokes.

On a day when his nearest rivals were fading, overnight leader Thomas stayed steady at Firestone Country Club in Akron, Ohio, producing two birdies and one bogey and finishing with a 15-under par total of 265. That left him four clear of American Kyle Stanley, who carded a two-under par 68 for 269. World number one Dustin Johnson and Denmark's Thorbjorn Olesen shared third place on 270, both storming home with six-under par 64s as those who began the day with higher hopes floundered. "I'm glad I finally played well around here," said Thomas, who claimed his first victory in an elite World Golf Championships event on a course where hasn't fared so well in the past.

The 25-year-old said he got "a little choked up" when he saw his grandparents in the crowd. His grandfather, Paul, played in the 1960 Championship at Firestone. "It's really cool," Thomas said. "They don't get to come out very often any more. This is my first PGA Tour win with them here, so that's pretty cool."

Northern Ireland's Rory McIlroy and England's Ian Poulter, who started the day sharing second three shots behind Thomas, both struggled. McIlroy's five bogeys included three on the trot at the eighth, ninth and 10th. His three-over 73 left him tied for sixth on 272. Poulter fired a four-over 74 that included a double bogey and five bogeys and left him in a group on 273.

Tiger Woods, an eight-time winner at the Firestone club hosting the Bridgestone for the last time, carded his second straight 73 to finish with a share of 31st. His last nine holes saw two double bogeys, three bogeys, three birdies and just one par. 

The tournament's final edition at Firestone offered little drama as no one got within two of Thomas. The American, who won twice early this season before hitting a dry spell that included a missed cut at the British Open, will defend his PGA Championship title at Bellerive in St. Louis, Missouri, in the final major of the season starting Thursday.