Rickie Fowler and Hideki Matsuyama shared fifth place on five under with Kevin Kisner, who needed to eagle the 18th to force a play-off but ran up a double bogey, dropping back into a tie for seventh with Graham DeLaet.

England's Jordan Smith, playing in his first major championship, carded a closing 68 to finish a tie for ninth with Open runner-up Matt Kuchar and former world number one Jason Day.

Spieth and Fowler were waiting beside the 18th green to embrace Thomas before he signed his card to claim the first prize of 1.89million US dollars (£1.4million) for his fourth win of a remarkable season.

The 24-year-old, who became the youngest player to shoot 59 on the PGA Tour on his way to winning back-to-back events in Hawaii in January, began the final round two shots off the lead held by compatriot Kisner.

And his chances of following Open champion Spieth as a major champion took an immediate blow when he thinned a bunker shot on the first across the green and into another bunker.

After bouncing back immediately with a birdie on the next, Thomas dropped another shot on the third before getting back on track with birdies on the seventh and ninth.

Another birdie did not look on the cards as Thomas hooked his drive on the par-five 10th, but the ball bounced off the trees and back into the fairway, from where he was almost able to find the green.

After chipping to eight feet Thomas saw his birdie putt hang on the edge of the hole for nearly 10 seconds before it eventually dropped in and took him into a five-way tie for the lead.

That tie lasted just a few minutes as Matsuyama, Kisner, Chris Stroud and Molinari all dropped shots, with Thomas then chipping in for birdie on the 13th to move two shots clear.

Thomas saw his two-shot lead cut in half as first Reed, then Matsuyama and Kisner, all picked up shots on the 14th and 15th to reach seven under par.

But Reed could only bogey the 18th after finding sand off the tee and Thomas holed from 15 feet on the 17th to increase his lead, before Matsuyama and Kisner both bogeyed the 16th.

That meant Thomas could afford to bogey the last and leave Kisner to try to play the last two holes in two under par, only for the 33-year-old to pull his approach to the last into the creek which runs the length of the hole and double bogey.

Fittingly in a tournament which invites 20 club professionals to compete, both Thomas's father Mike and his grandfather Paul were PGA professionals.

"I really can't put it into words," Thomas said. "I wish my grandpa could be here to see it. It's so special to get it done with three generations of PGA members.

"The putt on 10 was funny because it snuck up on the hole. We read it going back a little back right and it never did. I kind of acted like a child and threw a little tantrum, but then it went in and I didn't look so dumb."

Thomas went into the final day of the US Open in June just a shot off the lead after setting a tournament record for lowest score in relation to par with a nine-under 63 in the third round.

But he could only finish ninth after a closing 75 and said that experience played a large part in his victory at Quail Hollow.

"I felt like at the US Open, although Brooks (Koepka) had an unbelievable round, I needed to be more patient to have a better finish," Thomas said. "I felt like I had the game to get it done."