Justin Thomas enjoyed the perfect preparation for the defence of his US PGA Championship title with victory in the WGC-Bridgestone Invitational in Akron.

Thomas took a three-shot lead into the final round at Firestone Country Club and carded a closing 69 to finish 15 under par, four shots ahead of fellow American Kyle Stanley.

World number one Dustin Johnson surged through the field with a closing 64 to finish a shot further back alongside Denmark's Thorbjorn Olesen, who birdied three of the last five holes to also shoot 64.

Rory McIlroy and Ian Poulter had been Thomas' closest challengers at the start of the day but shot disappointing rounds of 73 and 74 respectively.

The Open Championship - best pictures Show all 43 1 /43 The Open Championship - best pictures The Open Championship - best pictures The Open Championship 2018 Golf - The 147th Open Championship - Carnoustie, Britain - July 22, 2018 Italy's Francesco Molinari kisses the Claret Jug after winning the 147th Open Championship REUTERS/Andrew Yates ANDREW YATES REUTERS The Open Championship - best pictures The Open Championship 2018 Golf - The 147th Open Championship - Carnoustie, Britain - July 22, 2018 Italy's Francesco Molinari celebrates with the Claret Jug after winning the 147th Open Championship REUTERS/Andrew Yates ANDREW YATES REUTERS The Open Championship - best pictures The Open Championship 2018 Italy's Francesco Molinari kisses the trophy as he poses for pictures with the Claret Jug, the trophy for the Champion golfer of the year after winning the 147th Open golf Championship at Carnoustie, Scotland on July 22, 2018. 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Thomas was far from his best as he played the opening 12 holes in level par and both Stanley and Jason Day eventually closed to within two shots, only to each promptly bogey the next two holes.

And a birdie from 12 feet on the 13th effectively sealed a first World Golf Championship title and the winner's cheque of £1.3million for Thomas ahead of the final major of the season at Bellerive Country Club.

"It feels awesome," Thomas, who has now won eight times since October 2016, said. "We did such a great job today of sticking to our game plan. It was a lot more difficult, a lot firmer and I didn't quite hit it as well today but we just had such control of everything.

Thomas carded a closing 69 to seal the title (USA TODAY Sports)

"My one bogey was when I just got a bad lie around the green, but I just made bogey and moved on and a very clean card."

An emotional Thomas was greeted beside the 18th green by his grandparents and added: "It's the first time I've ever cried after winning a tournament, but it was pretty cool having grandma and grandpa here."

Tiger Woods had earlier struggled to a closing 73 which contained six birdies, five bogeys and two double bogeys in the space of three holes on the back nine.

Thomas poses with the Gary Player Cup (Getty Images)

But the eight-time winner at least signed off in style with a birdie on the 18th, his last shot at Firestone Country Club before the event moves to TPC Southwind in Memphis next year.

"How about that huh?" Woods said. "I've made a few birdies there. It was a good way to end it. I'm going to miss this place. I've had so many great memories and it's just sad that we're not coming back here anymore.