Aussie tennis coach Darren Cahill plots Ash Barty's Australian Open downfall

Medvedev slams Australian crowd for lack of respect (0:37)

Daniil Medvedev hopes the home crowd will "respect both players" in future matches at the Australian Open. (0:37)

He's hardly her secret weapon but Darren Cahill has emerged as Amanda Anisimova's chief ally in the American prodigy's daring quest to crash the Australian Open Barty party.

After fighting off match points to oust defending champion Naomi Osaka in the shock of the Open, Animisova is now plotting to crush Ashleigh Barty's title dreams on Sunday.

And, behind the scenes, Cahill is quietly directing the show, perfecting the villain's lines after linking up with Anisimova for a coaching trial that has already reaped huge rewards this summer.

Having guided Lleyton Hewitt, Andre Agassi and Simona Halep to the top ranking and a swag of Grand Slam titles, the genie is very much out of the bottle when it comes to Cahill's unrivalled coaching credentials.

Little wonder former world No. 1 John McEnroe is applauding Anisimova's luring of South Australian Cahill as the 20-year-old continues her revival after the sudden death of her father two weeks shy of her 18th birthday.

"Really happy for Anisimova, she's been through some tough times," McEnroe told Eurosport.

"She might be like Sharapova as a great ball striker but she doesn't move as well as some of the top players.

"The biggest change I've seen in her in the last month or two is the presence of Darren Cahill.

"He coached Lleyton Hewitt, Andre Agassi, Simone Halep. Well, guess what? All three of them reached world No. 1 in the world.

"So this has been something Anisimova's been looking for, the right person to take her and get her where she belongs, which I believe is in the top 10.

"So this is a fantastic hire by her, a great moment for Amanda."

McEnroe is also happy for Cahill, his long-time commentary colleague at ESPN.

"He's a strategist - a lot of players have been giving Darren Cahill a call. He's been waiting for the right moment and this just seems to click beautifully," McEnroe said.

"It's been tough for him, he's been away from his family for six or eight months last year because of the pandemic.

"He's an example of a guy who had to quarantine twice, and that'll toughen you up and make you appreciate being on a tennis court.

"He's got a great attitude and he certainly knows the game inside out, and you saw her willingness to fight again out there against Osaka.

"Number one, just the mere fact that he's been around players who've reached the top and succeeded in a big way, that alone will give her big confidence."

And that little boost in confidence may be the difference that helps Anisimova over the line against Barty.

The one-time world No. 21 already knows she has the weapons to beat the top seed, having gone harrowingly close to toppling Barty in an epic 2019 French Open semi-final.

Barty often credits her great escape that day in Paris, after blowing a 5-0 first-set lead and then rallying from 3-0 down in the second to snatch victory before claiming her maiden Grand Slam crown, as a major career turning point.

Now the "great addition" of Cahill in her courtside box could be the turning point for Anisimova.

"He tries to help me stay calm and relaxed and just give me the confidence to just believe in myself and knowing that I can do it," Anisimova said.

Barty or Anisimova will play Greek fifth seed Maria Sakkari or American Jessica Pegula in the quarterfinals.