Justin Thomas celebrates his title victory ©Getty Images

Justin Thomas ensured a perfect preparation for the defence of his US PGA (Professional Golf Association) Championships title by winning the World Golf Championship (WGC) Bridgestone Invitational in Ohio.

The American built on his lead heading into the final round to triumph by four shots at the Firestone Country Club.

He shot a one-under-par 69 to finish on 15 under for the tournament. 

Fellow American Kyle Stanley finished 11 under in second place.

Denmark's Thorbjorn Olesen and American Dustin Johnson were a further shot behind in a tie for third.

"It feels awesome," Thomas said afterwards. 

"I did not hit the ball as well today but we had so much control and I had a very clean card at the end.

"It is the first time I have cried after winning a tournament. 

"It was pretty cool to have my grandma and grandad watching me."

Kyle Stanley finished in second place ©Getty Images
Kyle Stanley finished in second place ©Getty Images

Thomas led Northern Ireland's Rory McIlroy and England's Ian Poulter by three shots overnight, but the duo struggled through the final round.

McIlroy ended in a tie for sixth place after a three-over-par 73.

Poulter was tied 10th after a four-over-par 74.

The US PGA Championship is scheduled to begin on Thursday (August 9).

It will be the final major of the year.