Madison Keys leads 5-4 in the third set, and with another heavy return she pressures the best tennis player in the world into an error. It is 0-15 on a cool evening in Melbourne, and the American is three points from a first grand slam title.

The 29-year-old has spent more time on the professional tour than not, after debuting soon after becoming a teenager. She was a prodigy always destined for great things, until the years without a major triumph eroded expectations. At Rod Laver Arena she is now closer than ever to her fading destiny.

Then – in a blink – world No 1 Aryna Sabalenka holds serve. Across the net from the No 19 seed is a woman described by Keys’ own coach and husband Bjorn Fratangelo as “a little more of the polished version of Madison”. The Belarusian is three years Keys’ junior, yet is chasing a hat-trick of Australian Open titles and a fourth grand slam. And she broke the American’s heart in the semi-finals at the US Open two years ago, coming back from a set down.

On the blue court Sabalenka considers home, they are level again at 5-5 and Keys is back to square one. It’s a place the American has been many times. Eight years ago she was beaten in her only appearance in a grand slam final, at the US Open, failing to win a single game in the second set.

On Saturday night, the first point on Keys’ serve brings an error, handing her opponent the initiative.

The American reached No 7 in the world as a 21-year-old. She hasn’t been there since, hanging around on the fringes of the top 10 but never taking that next step. It was clear even to her time was running out. Turning 30 in three weeks, the American admitted during the tournament, has been on her mind: the end far closer than the start. A year ago Keys couldn’t play the Australian Open due to a shoulder injury. She made tweaks to her technique in a bid to bring longevity. She even changed rackets.

Serving now on Rod Laver Arena, she is down 15-30 and Sabalenka is two points from what would surely be a decisive break.

Keys, however, is different. She has said she has spent considerable energy working on the mental side of her game. She convinced Fratangelo to coach her, and married him late last year, on a day she has described as the happiest of her life. She has already beaten No 2 seed Iga Swiatek in the tournament, won four three-setters.

Keys produces a big serve for 30-30 but then the next return from Sabalenka is rifled back at her feet. The American does what she has been doing since she asked for a Serena Williams dress as a pre-schooler. She swings, launching the ball back down the line and into the corner, producing the tournament’s defining moment. Seconds later Keys holds for 6-5.

“Honestly, my only goal was to make sure that I played how I wanted to play, and not have any regret,” she said on Channel 9. “The US Open final that I lost, and then the last time I played Sabalenka at the US Open, I walked off the court, and I had a lot of regret because in the big moments, I felt like I kind of backed off.”

The next game, Keys’ liberated backhand puts her up 0-15. A clean winner on the return makes it 0-30. “I was going to absolutely be okay if I played how I wanted to and she beat me. If that’s how it happens, then no problem,” she said. “But that was my only goal.”

At 15-30, Keys hits a forehand that surprises Sabalenka into an error. “Once I was able to hold and go up 6-5, I just kind of said to myself: ‘Okay, no matter what there’s a match tie-break, you’re still in this. Just go for it,” Keys said. “And I just fully trusted myself.”

On the second championship point she launches a backhand return and the world No 1 is on her heels. One forehand and then two, Keys finds a winner.

Now she is spinning with her arms up and then on her head, not knowing where to look, what to do. Finally Keys – once lost, now found – walks to the net, Australian Open champion.