Australia's Jason Day has ended a long wait for his first major, shooting a final round 67 to clinch victory in the PGA Championship by three shots.

He led by three shots at the turn and held his nerve through the back nine to seal a memorable win over America's Masters and US Open champion Jordan Spieth at the Whistling Straits course in Wisconsin.

Sorry, this video has expired Emotional finish for Jason Day as he takes out PGA Championship ( Courtesy Fox Sports )

South Africa's Branden Grace shot a 3-under 69 to finish third on 15-under, while England's Justin Rose finished a shot back in fourth after a 2-under 70.

Day's four-round total of 20-under was a record low score for a major championship.

He became the fifth Australian to win the PGA Championship, after Jim Ferrier (1947), David Graham (1979), Wayne Grady (1990) and Steve Elkington (1995).

The win moves him to number three in the world, while runner-up Spieth becomes the new world number one, replacing Northern Ireland's Rory McIlroy.

"It's been a long journey, I didn't expect to ever grow up and be on the PGA Tour," Day said.

"It's an amazing feeling, this has been a dream since I've been 12 years old — to stand up in front of a crowd like this and hold the PGA [title] is really special.

"I didn't expect to cry. A lot of emotion came out.

"I've been so close [to a major] so many times.

"To play the way I did ... I could tell that he (Spieth) was the favourite, and to play the way I did and to finish the way I did was special."

The Beaudesert-native had been close in majors before on numerous occasions, most notably the 2013 Masters when he held a two-shot lead on the 16th tee before bogeying consecutive holes to finishing two shots out of a playoff between Argentina's Angel Cabrera and eventual winner, Australia's Adam Scott.

When the final round began Day was on 15-under, leading by two shots from Spieth, with Grace and Rose a further stroke back on 12-under.

Grace started strongly, going 4-under for the round by the seventh, but a run of three straight birdies from the fifth — including a monster putt on the seventh — saw Day blunt the South African's charge to go to 19-under, still three shots clear.

Jason Day's monster birdie putt on seven set him on the way to his first major title win at the PGA Championship. ( Getty Images: Jamie Squire )

Spieth had three birdies in the first six holes but a bogey on the fourth hurt his chase.

A bogey on eight dropped Day back to 18-under, and then an inexplicable muffed iron shot from the fairway on nine had the nerves jangling.

But he made a brilliant recovery to save par, while Spieth bogeyed, and Grace double-bogeyed the 10th to give the Australian a brief four-shot buffer.

Rose cut the lead to three with a birdie on 10, then Day birdied the 11th to get back to 19-under, three shots ahead of Rose, who backed up with another birdie on 11.

Day birdies 14 to strike blow to rivals

On the 14th, Day's tee shot went into a bunker, while Spieth was on the fairway.

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But the American dragged his approach to the left of the green while Day's shot rolled back down from the edge to give him a birdie chance.

Spieth got up and down with a great par putt, but the Australian sank his birdie putt from 15 feet to go 20-under and a four-shot lead with four to play.

Day tugged his tee shot left into the rough on 15, while Spieth hit the fairway.

The American gave himself a long birdie putt but missed, while Day did not get enough of his third shot from the back of the green and ended up bogeying the hole to reduced the margin to three shots with three to play.

Rose birdied the par-five 16th to go to 15-under, but holes were running out for the Englishman.

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Day and Spieth both hit good tee shots on 16, but the American hit his second into a bunker, while Day's approach caught the ridge at the edge of the green and stayed on.

Spieth had a terrible stance in the bunker, but somehow hit out to a couple of feet, while Day missed an eagle putt but matched Spieth's birdie.

Day lagged a very long birdie putt stone dead on the 17th, and Spieth also parred the hole to give the Australian a three-shot cushion going down the last.

Both players hit the fairway with their drives on 18, and once Day hit his approach to the par-four onto the green, victory was virtually assured.

Day was already in tears after lagging his birdie putt to within a foot, and once Spieth holed out for a par for a 17-under total, it was left to the Australian to tap in to become champion.

He embraced his wife Ellie and son Dash at greenside before heading in to the scorer's tent.

In winning, he denied Spieth the chance of becoming the first man since Tiger Woods in 2000 to win three majors in the same year.

Australian Matt Jones, who led at halfway, finished with a 3-over 75 for a 7-under total, tied for 21st.

His compatriot Cameron Smith had a 1-under round of 71 to finish 5-under for the tournament, tied for 25th.

The rounds of the day were 6-under 66s from American Brooks Koepka, who finished tied for fifth on 13-under, and Sweden's David Lingmerth, who finished tied for 12th on 10-under.