MELBOURNE: As Ash Barty was ascending the ranks of women's tennis, renowned Australian coach Darren Cahill regularly predicted the Queenslander was a champion in the making.

Leading into the 2019 Australian Open, when Barty was still to reach a Grand Slam quarter-final, Cahill described her as "the real deal" and she ended the year as world number one having claimed a maiden major title at Roland Garros.

But now, working with Amanda Anisimova, the champion coach is tasked with plotting the downfall of the player seeking to become the first local to win the Australian Open since 1978.

Anisimova ended the Australian Open defence of Naomi Osaka with a stunning upset on Friday night and will now play Barty in the fourth round on Sunday.

While commentating on Australian television on Friday night, Cahill downplayed the impact he has had on Anisimova, noting he had only been part of her team for a month.

Barty powers into clash with giant-killer Anisimova

But American John McEnroe said on Eurosport he is certain Cahill, who coached Simona Halep, Lleyton Hewitt and Andre Agassi to the world's top ranking, has already helped her.

Romanian Halep, who parted ways with Cahill last season after a six-year partnership, said the Australian was the most important person in her career.

"With him I could achieve the big titles. He also taught me how to be a better person out of the court, to enjoy more life," said the twice Grand Slam champion, who reached the fourth round at Melbourne Park on Saturday.

"My coach now is a great person as well. I feel good with them. But I do miss Darren."

With Wimbledon winners Halep and Barty practising together regularly, Cahill has watched world number one Barty closely in recent years.

Florida resident Anisimova, 20, is unbeaten this year and claimed the Yarra Valley Classic the week prior to the Australian Open.

"He's been a great addition to my team the last couple of weeks," Anisimova said.

"He tries to help me stay calm and relaxed and ... does a great job of, you know, telling me those things."

With Osaka out of the way, Barty's path to the title is clearer and she has won 14 of the 18 matches she has played against the women left in the top half of the draw.

That includes a victory over Anisimova in the semi-finals of the French Open in 2019.