Niemann cashed in with an eagle at the second extra hole after a trio of big-name local hopes let the famous trophy slip during a wild final round in Sydney.

Starting the day four shots from the lead, Niemann – who plies his trade on Greg Norman's Saudi-backed breakaway league after defecting from the PGA Tour – stormed home with a final-round five-under-par 66.

Five birdies and a lone bogey on the back nine saw the Chilean rattle home in 32 and set the clubhouse mark with the final group still more than an hour from finishing. He is the first South American golfer to hoist the Stonehaven Cup and it also brought Niemann's win drought to an end.

"It means a lot," Niemann said. "I wanted to win so bad for a long time. The last one I have is in Riviera, and yeah, I mean this season wasn’t the best season that I play on LIV. I haven’t had a great finish and after the season I kind of start working a lot harder with my coach and all my team and and started seeing a bit of results.

"I mean, I wanted to play more golf because I felt like I was kind of like finding my game. It was getting better. I was hitting better, putting better and I was like ‘I want to go out and play and see if it’s true, you know?’ 

"Then I had these two weeks in Australia and actually was a really easy decision, I was in Chile, flight from Chile to Sydney which is really good and obviously there are world ranking points, which I think I need a few now and the open spots here this week, so I was really happy to see some golf."

Hoshino closed with a 70 to make the playoff at 14 under but wound up second for the second Sunday running, having last week finished three shots behind West Australian superstar Min Woo Lee at the Australian PGA.

Lee will be ruing not saluting again after he entered the final round as co-leader with Hoshino and in the form of his life.

Joaquin Niemann makes eagle and claims the Australian Open title. PHOTO: Getty Images.

And former World No.1 Adam Scott and fellow U.S PGA Tour star Lucas Herbert also had one hand on the Stonehaven Cup at different stages during Sunday's last round.

But all three fan favourites suffered heartbreak, as did Lee's superstar sister Minjee, who had to settle for the runner-up prize in the Women's Open after South African Ashleigh Buhai defended her title with a thrilling one-shot win.

While Lee relinquished his lead early, Scott and Herbert had turns at looking likely winners down the stretch, only to falter in incredible fashion.

In the space of seven depressing minutes for Australian golf fans, both suffered triple-bogey sevens to see their hopes vanish.

Rikuya Hoshino escapes the pine straw to set up a birdie on the final hole. PHOTO: Getty Images.

From 14 under and outright leader with three holes to play, Scott – who started his round on the 10th – drove out of bounds on the par-4 7th hole.

Having played a provisional tee shot, he couldn't make par with his second ball and suddenly tumbled to 11 under.

"I think if it was the last hole, I might have stormed off," Scott said after adding his tie for fourth – three shots out of the playoff – to a trio of runner-up finishes since winning the Open for the only time in 2009.

Moments after Scott's mishap, Herbert, also at 14 under, found the trees on the 9th and recorded his own gut-wrenching triple-bogey. He never recovered.

"It was super frustrating because you'd hit decent shots and get punished," Herbert said of the gruelling last-day conditions.

"I didn't do a lot wrong. I missed a short putt, I blinked and made triple. It's hard to see your name fall out of the lead like that."

Min Woo Lee gets frustrated with a cold putter during the latter stages of the final round. PHOTO: Getty Images.

As much as Scott's and Herbert's crashes hurt, Lee will likely rue the one that got away most.

Bidding to join an elite group of only six players, including legends Greg Norman (1985), Peter Thomson (1967) and Kel Nagle (1959) to have completed the Australian PGA and Open same-year double, the 25-year-old may never have a better chance.

But Lee was philosophical about falling two shots short of at least making the playoff with his closing 72.

"The putts didn't go my way and I didn't hit it well enough," Lee said.

"I was up and down from literally everywhere. It's not good enough to win a tournament.

"But it's been a good year and I'm pretty proud of the way I've finished."

There was a significant consolation prize for Scott, who booked his place next year's Open Championship at Royal Troon with his T4 finish. Niemann and Hoshino also claimed places in the field for the 152nd Open.

For Niemann, he now knows he will be playing The Open but is unsure whether he, as a LIV Golf player, will get a start in the other majors.

"I know for sure I’m playing the Open, which is nice and yeah, it is unfortunate I think I should be playing those tournaments," Niemann said. "I know I have a game to win one of the Majors and yeah, I mean, but it is what it is.

"I took this challenge of knowing that I was not going to be in the Majors, so I was going to go out there and try to get my spot and that was kind of like my mentality of coming here to Australia. I mean, I want to get a spot. I want to be in the Open and I know at the Open I can have a chance, so it’s nice to know I have that chance now."

He also has the chance to win tournaments in consectuive starts as he will be the main drawcard for the upcoming Chile Open.

– Darren Walton, additional reporting from Brendan James