Thomas led Rory McIlroy and Ian Poulter by three shots overnight, and the Northern Irishman and Englishman tailed off in the final round.

McIlroy ended in tied sixth place after a three-over-par 73, while Poulter was tied 10th after a four-over 74.

Thomas finished on 15 under after a one-under 69 on the final day.

"It feels awesome," he said. "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."

Fellow American Kyle Stanley finished second on 11 under, with Denmark's Thorbjorn Olesen and American Dustin Johnson a further shot behind in tied third.

The US PGA Championship - the final major of the year - begins on Thursday.

Elsewhere, England's Georgia Hall won her first major title with a two-shot victory at the Women's British Open at Royal Lytham and St Annes.