26/11/2017 7:27 PM AEDT | Updated 26/11/2017 7:27 PM AEDT

Stunned Davis wins Australian Open after Day blows up

"This is a dream come true," he said. "I'm going to remember this forever."

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Cameron Davis of Australia poses with the Stonehaven Cup during day four of the 2017 Australian Golf Open at the Australian Golf Club in Sydney, Australia.

SYDNEY (Reuters) - Cameron Davis stunned even himself by shooting a seven-under-par 64 to win the 102nd Australian Open by a stroke on Sunday after overnight leader Jason Day's title charge ended in a mid-round collapse.

The little-known Australian holed out for an eagle from the fairway at the 12th and sank an eight-foot putt for his sixth birdie at the 18th to upstage not only compatriot Day but defending champion Jordan Spieth.

With five leading groups still playing when he signed for his 11-under 273, Davis was shocked that he had ended up with the Stonehaven Cup in his hands, $225,000 in the bank and a spot at next year's British Open.

"I'm a little bit numb at the moment, I just didn't expect to be in this situation," the 22-year-old told reporters.

"Even though I had a great round, I didn't think I was going to be far enough up the leaderboard. When I finished my round and had a look where everyone was, I was a bit surprised."

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Jordan Spieth of the United States reacts during day four of the 2017 Australian Golf Open at the Australian Golf Club on November 26, 2017 in Sydney, Australia.

Matt Jones, the 2015 champion and member of the host Australian Golf Club, shared second with Swede Jonas Blixt after both shot 68s in a dramatic final round.

Cameron Smith also shot a 68 to finish fourth on nine-under but none of them was able to mount a challenge to knock Davis off the lead as the Sydney crosswinds wrought their customary havoc.

Former world number one Day started the day with a one-stroke lead but calamity struck when his ball hit the edge of a bunker and dropped into the water for a double bogey at the ninth.

Two more dropped shots at the 11th and 13th effectively killed off his hopes of winning his home Open for the first time to end his 2017 title drought and he finished fifth on eight-under.

"I just didn't play my best and obviously it's not great to shoot two-over par on the final round when you've got the lead," Day said.

"You know what? It is what it is."

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Cameron Davis hits a tee shot on the 14th hole during day four of the 2017 Australian Golf Open.

American Spieth ended his title defense with an eagle at the 18th but his closing 67 was not enough to bridge the gap to the leaders and he ended up eighth on six-under.

"It was a great finish, it was nice," said the world number two.

"I felt like I hit a lot of really beautiful shots that weren't necessarily rewarded today based on just trying to judge the crosswinds. I really felt like I shot 62 today and it was 67, I had so many looks."

The day belonged to the man 1,492 places below Spieth in the world rankings, who etched his name onto an honor roll with Spieth, Rory McIlroy, Greg Norman, Jack Nicklaus, Gary Player and Peter Thomson.

The former Australian Open amateur champion, who turned professional last year, shot a 63 to lead after the opening round but had all but given up hope of a victory after following that with a 72 and a 74.

"This is a dream come true," he said. "I'm going to remember this forever."

(By Nick Mulvenney; Editing by Amlan Chakraborty)