Kentucky's Justin Thomas galloped to his maiden major victory at the US PGA after a thrilling final day that had more ups and downs than the Aintree Grand National.

After the gruelling slog of the first three days, softer conditions and friendlier pin positions transformed Quail Hollow from a theatre of pain into a five-ringed circus with 24-year old thoroughbred Thomas hoisting the giant Wanamaker Trophy aloft.

A former team mate of Mount Wolseley’s Gavin Moynihan at the University of the Alabama, he closed with a bogey for a three-under par 68 and a two-shot win over Italy’s Francesco Molinari, fellow American Patrick Reed and South Africa's Louis Oosthuizen on eight-under par.

Overnight leader Kevin Kisner needed an eagle two at the 18th to force a three-hole playoff but tugged his approach into the creek, finishing with a double bogey for a 74 and a share of seventh with Graham DeLaet on four-under.

The son and grandson of PGA professionals, an emotional Thomas stood next to the PGA of America officials and said: “I’m proud. I can’t put it into words. I have seen all these people so often, and they were probably annoyed by me running around family dining, six, seven, eight years ago at PGA Championships.

“I wish my grandpa could be here for it. It’s just so special to get it done with three generations of PGA members. I’m just glad we have a trophy now.”

Reflecting on the key to overcoming his final round failure in the US Open at Erin Hills, he said: “Just patience. I felt at the US Open that while Brooks [Koepka] had an unbelievable final round and I didn’t have my best stuff that day, I needed to be a bit more patient to have a better finish. 

“Obviously you play to win, and I had an opportunity to win today, but I knew that no matter where my game was at today, I just needed to be patient. I felt like I had the game to get it done and it was just a matter of whether I did or not.”

It was a final day to remember as Molinari shot a 67 to set the target at six-under par before being joined on that mark by Reed, who also shot 67, and then by Oosthuizen, who holed a 53 footer on the last for a 70.

Thomas made a crucial sand save at the 16th and was two ahead playing the 221-yard 17th where he rifled his tee shot to 15 feet and rolled in the birdie putt to take a three-shot lead to the last.

In the end, he hit his tee shot into a fairway bunker but found the green in three and two putted from 28 feet to become the eighth first-time winner in the last nine majors

There were as many as five players tied for the lead on seven-under par early on the back nine as Thomas joined Kisner, Chris Stroud, Matsuyama and Molinari on seven-under par.

Slowly they all fell away as major pressure, Quail Hollow's deep rough and the three-hole finishing stretch they call the Green Mile claimed its victims.

Yeah, it was a crazy day. Had to be an unbelievable watching today in terms of spectating and sitting at home watching on TV.

"I forget what hole it was, I think walking up to 12 green, there was maybe five of us at 7-under. I had no idea it was that close. I mean, I kind of thought Hideki and I were, you know, at around 7 or 8 or whatever he was, or 6 are 7, and then some other guys. Then I saw P-Reed was playing well. I saw Rick was kind of making a run. I saw Francesco was up there, and then obviously Kis and Stroud behind us. To see that was kind of crazy.

And then that chip-in on 13 was probably the most berserk I've ever gone on the golf course. I'm kind of interested to see how I looked for that. Yeah, it was nice.

"I hit a bad tee shot on 14, but got out there of with a good par, and then you know, I hit a good little pitch after I chunked a 5-iron, and then it just missed the putt on 15. I played 16, 17, 18 well all week, I felt like. Obviously I'm nervous, I want to win, but I was a lot of more comfortable and calm than I thought I would be.

"So just kind of going through those holes knowing that I've done this a million times. I know that's cliché and everyone says it. And Jimmy did an unbelievable job of keeping me calm. It was -- felt like it was a great, great team win for us."

Thomas (24) began the day two shots off the pace on five-under, made two bogeys and three birdies to turn at six under before watching an eight-footer at the 10th stop on the lip and teeter there for nearly 10 seconds before toppling in for a birdie.

The bogey he made at the first — he drove into a bunker 350 yards from the tee, found greenside sand and thinned his bunker shot into the sand on the far side before making a 14 footer — was crucial.

"That's a big moment, second to the last group, major, great chance to win. And I absolutely just blistered a drive, exactly. I picked up my tee and thought it was perfect, and it was in the bunker. It's like 350 to the bunker and I didn't think I could get there.

"I was a little bummed to walk up there and see that. I mean, I had an easy bunker shot, that first one. I just didn't have a very good lie. And I was just trying to chunk and run it, and obviously thinned it. I mean, I couldn't -- through four shots on that hole, I pretty much couldn't have drawn up a worse start to my Sunday at the PGA Championship.

'I felt great with my putter all week. I just, I stayed calm. I was like, I could still knock this in and if I don't, I have 17 more holes. It's not like this course, being two back, I had to go shoot 6- or 7-under. I knew 2- or 3-under had a pretty good chance. After rolling that in, it just kind of calmed me down and kept me going."

The Kentucky star won three PGA Tour events in his first five starts this season before shooting 59 in the Sony Open and a nine-under 63 in the third round of the US Open at Erin Hills to go into the final round just a shot off the leader before fading to tied ninth after a 75.

This time, he didn't falter.

After chipping in for a birdie two from the fringe at the 13th to move a shot clear on eight under par, Matsuyama dropped his third shot in row there to fall back to five under.

Bidding to become the first male Japanese player to win a major, the 25-year old world No 3 then birdied the 14th and 15th to get back within one but overshot the 16th and bogeyed, eventually carding a 72 to tied for fifth with Rickie Fowler.

Fowler set the clubhouse target at five under with a 67 rattling in four birdies in a row from the 12th before saving par from nine feet at the 18th to eventually finish on five-under.

Rory McIlroy finished tied for 22nd on one-over par after a 68 and revealed he is contemplating taking the rest of the year off to allow his rib injury to heal.

“He’s hurt and I am watching his golf swing deteriorate,” said former world No 1 David Duval.

"If only I could go back and tell myself 18-20 years go when I started having those problems, 'Stop, get healthy'. He could do himself a big service."

Shane Lowry closed with a one-over 72 to share 48th on five-over.