When words such as "tough", frustrating" and "tricky" are used to describe Ash Barty as an opponent, it is easy to see why the Australian sits atop the world rankings.
Barty already has two majors in her keeping — the 2019 French Open championship and last year's Wimbledon title — and she remains favourite to add another to her tally at Melbourne Park.
Her Australian Open campaign has so far been impressive. The 25-year-old is yet to drop a set and her serve has only been broken once.
And perhaps posing as an ominous warning for her US rival Madison Keys in tonight's semifinal on Rod Laver Arena, Barty's coach Craig Tyzzer feels his charge can still improve on her performances at the tournament.
Keys — a former world number seven and US Open finalist — will not be a pushover, as Barty and her "team" have acknowledged.
She has been in superb form in Melbourne, as illustrated by her convincing victories over seeds Barbora Krejčíková and Paula Badosa in her two most recent matches.
But while Keys is immensely talented, she will have to come up with a strategy to outwit Barty, whose game appears to have so few weaknesses.
"You feel pretty helpless," said Jessica Pegula, after she lost to Barty in the quarterfinals.
"I think that when she gets into a rhythm … her game just kind of picks you apart a little bit, and it can be really frustrating because you don't feel like you can get a lot of free points, there's really not much you can do.
"It doesn't feel good. It feels kind of helpless. I didn't feel there was a lot I could do and then even games where I was up really easy, I still didn't win the games.
"She just doesn't give you any free points."
Pegula could only win two games off Barty in Tuesday's quarterfinal, going down 6-2, 6-0 in just over an hour.
The American is no easybeat. She was seeded 21 in Melbourne and was an Australian Open quarterfinalist last year.
"I think she just does everything really well. Honestly, she just does everything, I think, a little bit better than everybody," she said.
Barty's 'variety' among her strengths
Pegula's countrywoman Danielle Collins — who plays Polish seventh seed Iga Świątek in the other semifinal — has triumphed in only one of her four matches against Barty.
Collins said Barty was not a one-dimensional player, which meant she could find several ways to win.
"I really admire Ash as a player," said Collins, who is the 27th seed at Melbourne Park.
Barty has won two of her three previous meetings with Keys, the most recent being in the 2019 French Open quarterfinals before she lifted the trophy at Roland Garros.
Pegula said Keys had the game to play Barty "pretty close" tonight, noting the power of her serve and forehand.
But she highlighted Barty could not be allowed to dictate terms, as that was when her opponents fall into her trap.
"Just to do it two out of three sets, for somebody to beat her (Barty) is tough because she just makes you play so much and does everything so well," Pegula said.
"I think she's definitely living in everyone's head a little bit. I don't think anyone is going to feel great going out to play her because they know they have to play really well."
