AKRON, Ohio — Nervous at the start, Justin Thomas was in full control at the Bridgestone Invitational to the end. He had a four-shot lead and faced a 15-foot birdie putt on the final hole that would only determine his margin of victory.

And then he nearly lost it.

He marked his ball, turned toward the back of the green and saw his grandparents, Paul and Phyllis Thomas, who had never seen him win since his joined the PGA Tour.

Paul Thomas is a career club pro who played himself at Firestone in the 1960 PGA Championship. His grandmother is one of his biggest supporters who navigated her way around the hills of Firestone using a walker in 90-degree heat.

Thomas bowed his head to collect his emotions, which were stronger than when he won the PGA Championship last summer.

“I just got a huge knot in my throat and I just had to put my head down,” he said after closing with a 1-under 69 for his first World Golf Championship title. “I’ve never gotten like that on the golf course before. You just don’t know if they’re ever going to see me win if I don’t win here. So it was pretty cool to get it done.”

They saw a one-man show that sent Thomas to Bellerive Country Club in St. Louis with high hopes of joining Tiger Woods as the only back-to-back winners of the PGA Championship in stroke play.

Playing in the final group with Rory McIlroy, the 25-year-old Thomas never let anyone closer than two shots of the lead. He opened made only two birdies and left the mistakes to everyone with range of him. McIlroy finished the front nine with consecutive bogeys and never recovered. Ian Poulter started three shots behind and shot 74. Jason Day made a run with three straight birdies to start the back nine, only to play the final six holes in 5-over par for a 73.

Tiger Woods was never in the picture.

In the final World Golf Championship at Firestone, on the South course where Woods set a PGA Tour record with eight victories, he tried to end with a bang and turned in a dud. Woods made two double bogeys and three bogeys on the back nine and salvaged a 73 to finish 15 shots behind.

“Things could have certainly gone better,” Woods said. “But it is what it is, and on to next week.”

Thomas could not have asked for a better week. Winless the last five months without feeling as though his game were in disarray, he got the result he needed ahead of the final major of the year. He joined Dustin Johnson and Bubba Watson as three-time winners this season.

He lost in a playoff at the Mexico Championship. He lost in the semifinals of the Match Play. At the Bridgestone Invitational, he became the 21st player to win a World Golf Championship and a major.

“It was kind of one of the few things left that I felt I needed to knock off or felt that would have been nice to add to the resume, for sure,” Thomas said. “To win on a golf course like this, a championship golf course and always against a very tough field, it just felt great.”

Sweetest of all was seeing his grandparents, especially the embrace after he tapped in for par to finish at 15-under 265. Thomas turned his head and placed it comfortably on his grandfather’s shoulder.

So ended a finale at Firestone that otherwise lacked drama. Thomas had not finished better than a tie for 28th in his two previous appearances at Firestone. He wound up winning the last one.

“I’m glad I finally played well around here, just in time to leave,” he said.

Firestone has held tour events since the Rubber City Open in 1954. The World Series of Golf began in 1962, and it became an official PGA Tour event in 1976. In many respects, it was the precursor to the World Golf Championships by bringing in winners from around the world.

Bridgestone shifted its title sponsorship to the PGA Tour Champions, which will bring its Senior Players Championship to Firestone next year. The World Golf Championship instead will move to Memphis, Tennessee.

Kyle Stanley got within two shots of the lead until bogeys on the 13th and 14th holes. Stanley closed with a 68.

Johnson, the world’s No. 1 player who was coming off a victory in the Canadian Open, started the final round 10 shots behind and shot 29 on the front nine. A birdie at No. 10 put him three shots behind, but that was all he had.

Johnson bogeyed the last hole for a 64 and shared third with Thorbjorn Olesen of Denmark, who also had a 64.

Thomas won for the ninth time in his career and moves to No. 2 in the world, with a shot to regain the No. 1 ranking next week.