AUSTRALIAN Jason Day dumped his nearly man tag in the Majors by winning the US PGA Championship with a record score of 20-under-par.

The 27-year-old shot a closing 67 at Whistling Straits on Sunday to record the lowest total at one of golf's four majors - beating Tiger Woods record of 15 years ago.

Justin Speith, who was aiming to win three Majors in a year, finished second but with the consolation of becoming the world number one, ending Rory McIlory's reign.

South African Branden Grace was third on 15-under and Justin Rose of England finished fourth on 14 under after his challenge faded with a double bogey on the 13th. McIlroy closed with a 69 to end his first tournament back from an ankle injury at nine under par.

An emotional Day enjoyed the "amazing feeling" of claiming his first major victory in the US PGA Championship after a number of painful near-misses.

After nine top-10s in his previous 19 majors, and just two months since collapsing due to vertigo during the US Open, Day was in tears even before tapping in for par on the 18th, where he was embraced by his caddie and mentor Colin Swatton, son Dash and wife Ellie, who is pregnant with the couple's second child.

"The path that I was on was never expected for me to be here where I was today," Day said. "I lose my dad at 12 and then meet Colin and have him walk the journey with me and have him walk up the 18th hole with me was just a special, special thing that I could never forget. It's just an amazing feeling I have.

"It's been a long journey. I never expected to be out here on the PGA Tour. It's an amazing feeling with the work that I have put in my game since I was 12 years old and to be able to stand here in front of a great crowd and win the PGA is pretty special.

"I did not expect I was going to cry! There's a lot of emotion because I have been so close so many times and fell short. To play the way I did, especially with Jordan in my group was just amazing."

Asked about surpassing the previous scoring record of 19 under par set by Tiger Woods in the 2000 Open, Day added: "I did not know that. That was a pretty amazing accomplishment.

"It's a fantastic record to hold. There's been such amazing golfers, especially throughout the history of golf, our sport, and to have that record just goes to show the work I've put in is paying off."

Spieth had the consolation of becoming the second youngest world number one behind Tiger Woods, overtaking defending champion Rory McIlroy, who finished 17th on his return from injury.

"It's by far the best consolation, by far the best loss I think I've ever had because I felt that I not only couldn't do much about it, as the round went on, I also accomplished one of my lifelong goals," Masters and US Open champion Spieth said.

"That will never be taken away from me now. I'll always be a number one player in the world. It feels really good. It's an unbelievable feeling.

''I knew walking up the 16th Jason was going to win so I was focusing on finishing second and accomplishing a career goal. So much work has gone into this and what a year it has been.''

Spieth was quick to pay tribute to Day, admitting he was surprised at how aggressively his playing partner had attacked the course.

"It was fantastic," Spieth added. "We play a lot of golf and we played a lot of major championship rounds together and that was the best I've ever seen him play.

"Just given the timing of it and whatever, he's impressive to watch strike the ball, but it was nothing like today. He took it back and he wailed on it and it was a stripe show. It was really a clinic to watch.

"As he pulled driver late in the round, I kept having hope, as he took it back, that maybe one of these drives he'll miss and he'll get a bad break and maybe he'll have a double (bogey) and it will just startle him.

"I just never had the opportunity to really control the round today, even in the middle of that round I could have made up a couple more shots, gotten it to maybe one shot or two with six holes to go. But he still was in control. He was still making birdie on the holes that I didn't birdie so I wasn't going to gain that much momentum."