Melbourne (AFP) - Ashleigh Barty is wary of “exceptional athlete” Madison Keys but the resurgent American knows she will need more than supreme fitness to outsmart the top seed and make the Australian Open final.

Barty is renowned as one of the best tacticians in the game and has out-thought and out-played all her opponents so far, in devastating fashion.

Heading into their semi-final on Rod Laver Arena on Thursday, the world number one has dropped just 17 games in her five matches at Melbourne Park without losing a set.

As well as “problem-solving” her way out of tricky moments, Barty has developed an exceptional all-court game which beaten quarter-final opponent Jessica Pegula said “picks you apart”.

The unseeded Keys, who made the last four in 2015 and lost to eventual champion Serena Williams, said it was important for her to “continue to focus on my side of the net”.

But she also knows Barty’s dangerous backhand slice – which courtside interviewer Jim Courier compared to Roger Federer – must be blunted.

“I think she does such a good job at resetting the point constantly, being able to get back to neutral off of a ball,” she said.

“You can’t do a ton off of her slice because it comes in so low.”

Two-time Grand Slam winner Barty is aiming to become the first Australian woman to win her home Grand Slam since Chris O’Neill in 1978 and will start as favourite.

But the down-to-earth Australian is taking nothing for granted against a player who has beaten 2020 champion Sofia Kenin, eighth seed Paula Badosa and fourth seed Barbora Krejcikova.

“Maddie is an exceptional athlete, she has a great serve, great first strike off the return and off her first ball after her serve,” she said.

“A lot of the time it’s about trying to put her in an uncomfortable position, try and get her off-balance, because if she controls the centre of the court the match is on her racquet.”

- ‘It’s gonna be hard’ - -

In the second semi-final, Polish seventh seed Iga Swiatek faces 27th-seeded American Danielle Collins, who is enjoying a second wind after surgery took away the pain that was hampering her game.

Big-hitting Collins said she expected the 2020 French Open champion to be “very relentless, powerful, strong”.

But after making the semis at Melbourne Park in 2019, the 28-year-old believes she now has the experience to press on.

“Now that I’ve made quarter-finals at French and semi-finals here before, I think I can use those experiences to certainly help me in the tight-pressure moments on court. I can use that to my advantage,” she said.

“Last time I was here in the semi-finals I had never done that before. Hopefully I can carry the confidence that I’ve gained over the last couple years and be able to use that to my advantage.”

Swiatek is still just 20 but has also gained huge experience since her French Open triumph, and is in the second week for a sixth consecutive Grand Slam.

But this is the first time she made the last four away from the Paris clay.

“I will approach it the same as any other match, really. I have played with some heavy hitters in this tournament already, so I feel like I’m feeling their game on my racquet pretty well,” she said.

“For sure it’s gonna be hard, and she’s in great shape, you can see that, and really confident. But I also feel that way.”

Ranked nine, Swiatek is projected to move to fourth in the world and could go as high as three if she wins the title.