Denmark's Caroline Wozniacki beat Romanian Simona Halep to win her first Grand Slam title and regain the number one ranking at the Australian Open.
The second seed won 7-6 (7-2) 3-6 6-4 in punishing conditions to finally land a major title at the 43rd attempt.
Nine years after her first Grand Slam final defeat, and 17 months after she was ranked 74th, the Dane was overcome.
"I dreamt of this moment for so many years, and to be here today is a dream come true," said Wozniacki.
The victory means the 27-year-old will replace Halep as number one in the world rankings on Monday.
Twice a runner-up at the US Open, Wozniacki becomes the first Dane to win a Grand Slam singles title.
Halep, too, had been hoping to end the wait for a first major title to add to her number one ranking, but she has now lost in the Australian Open final as well as two French Opens.
"Of course I am sad but Caroline was better than me," she said.
"I fight and have many years to go, so hopefully will face another challenge like today."
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Wozniacki grabs Grand Slam opportunity
The final might have been begun at 19:30 local time but conditions were brutal, with the temperature above 30C until well into the night and the humidity oppressive.
Both women had endured testing paths to the final, saving match points along the way, and at times looked on the point of exhaustion in a gripping final set.
Wozniacki deservedly took the opener in a tie-break, having let a 4-1 lead slip, and Halep appeared in trouble when she required treatment from the doctor midway through the second set.
However, after having her blood pressure taken, the Romanian returned to take three of the four next games, levelling at one set all with a forehand winner.
The heat rule was in effect should either player wish to use it, and Halep took the chance to halt proceedings for 10 minutes and allow both finalists to head off court in search of air-conditioning.
Halep had now spent over 13 hours on court during the tournament, while Wozniacki - who saved two match points against Jana Fett in round two - was approaching 12 hours.
The final set was a huge test of mind and body, and it produced some thrilling tennis.
After twice breaking serve to edge ahead, Wozniacki looked to have let another Grand Slam chance slip away when she fell a break down at 4-3 in the decider and needed treatment to a knee injury.
Instead, Wozniacki was the one who grabbed the moment, playing superbly in the final three games.
With Halep now serving to stay in the contest, Wozniacki's brilliant defensive skills eventually forced an error on match point, leaving the Dane flat out and tearful on the Rod Laver Arena court.
'I want to thank my dad'
Wozniacki has spent 67 weeks at number one in her career, but it had been six years to the day since she last reached those heights, and four years since her second and last Grand Slam final.
By the time her ranking had plummeted to 74th in 2016, few thought she would ever be in contention for the major prizes again.
A change of approach was required and in tandem with her father and coach, Piotr, they developed a more attacking style that has taken her back to the top of the game.
With more pace off forehand and backhand, a much improved serve, and a gameplan to go on the offensive rather than rely on her athletic defence, Wozniacki climbed back up the rankings.
Six runner-up finishes in 2017 showed progress, despite concerns over whether she could go the last step, but victory in Tokyo, and then the biggest win of her career at the WTA Finals, set her up perfectly for 2018.
"Last but not least, I want to thank my dad who has been there since I was seven," said Wozniacki.
"We've had ups and down, but you've been there every step of the way."
Wozniacki deserves success - analysis
BBC Sport tennis correspondent Russell Fuller
Twenty stroke rallies seemed almost the norm in this spellbinding contest. It was an enthralling match - packed with quality, tension and medical emergencies.
Wozniacki's achievements in the game have always been hugely respected. She has been a serial winner on the WTA Tour for a decade, but often considered to be lacking the X-factor or nerve to win a Grand Slam.
At the end of 2016, premature retirement appeared to be an option she was seriously considering. But on she played, and after losing six finals in a row, finished 2017 in style by winning the WTA Finals in Singapore.
And now she has broken her Grand Slam duck, by winning the last three games of the final set from a break down - having saved match points in the first week. Wozniacki has passed the Grand Slam test with distinction.
There is also a huge amount of sympathy for Halep, who was battling her ankle, leg and fatigue, as well as the Dane. Her enormous courage took her to within two games of the title.
Halep has the French Open to look forward to next, on her favoured surface of clay. And as she reflects on losing her first three Grand Slam finals, she should remember Andy Murray and Ivan Lendl both lost their first four. They currently have 11 Grand Slam titles between them.
|5/14||Break points converted||5/12|
|110||Total points won||108|
|Match time: 2 hours 49 minutes|
Wozniacki's route to the title
|First round||Mihaela Buzarnescu||6-2 6-3|
|Second round||Jana Fett||3-6 6-2 7-5|
|Third round||Kiki Bertens (30)||6-4 6-3|
|Fourth round||Magdalena Rybarikova (19)||6-3 6-0|
|Quarter-final||Carla Suarez Navarro||6-0 6-7 (3-7) 6-2|
|Semi-final||Elise Mertens||6-3 7-6 (7-2)|
|Final||Simona Halep (1)||7-6 (7-2) 3-6 6-4|