Keys declared beating Barty was tennis's version of Mission Impossible after being swatted aside 6-1 6-3 in an Australian Open semi-final mismatch on Thursday night.

A one-time US Open runner-up, Keys was merely Barty's latest victim in a summer rampage the like of which fans have never seen before from Australia's queen of the court.

Barty has conceded just 21 games in six matches en route to the final in the most rampant run through an Open draw since Steffi Graf dropped only 19 on her way to the title match back in 1989.

Looking untouchable, the hot Open favourite has also won 81 of her past 82 service games.

Little wonder Keys just shrugged and said "it sucks" when asked what it felt like playing Barty right now.

"It's tough. She's just playing incredibly well," the American said.

"You have a game plan in your head, but she's just executing everything so well.

"She's serving incredibly well, so you don't get any free points on that.

"Her slice is coming in so much lower and deeper than it was in the past - everything is coming in at your shoelaces on the baseline - so it's not like you can really do anything with that.

"Then you try to play to her forehand and she can open you up there ... she's doing a really good job at mixing up paces and spins, as well.

"It feels like you can't really get in a rhythm off of that forehand side.

"I mean, I have played her a handful of times and this is easily the best she's ever been playing."

Keys said it wasn't like Barty had surprised her at all with her game plan but rather that the Wimbledon champion was merely close to unplayable in her current mood.

"The tough thing is that I think she kind of makes you overthink a little bit - and you start pressing a little bit," Keys said.

"You feel like you have to do too much at times.

"I was overthinking a little bit at the beginning, trying to do things that weren't really happening for me or weren't really actually an option just because she kind of puts that pressure on you.

"I definitely was pressing a little bit and overthinking.

"Once that happens and I feel like when she starts feeling like she can play downhill, then she just gets that confidence and momentum and it's really hard to get that back from her."

Like Serena Williams, Roger Federer or Novak Djokovic in their pomp, every now and then a player comes along and separates themselves from the rest - and Keys claimed in the women's game that was Barty right now.

"She seems very focused but she's playing very within herself," Keys said.

"And it just seems like everything is really working for her right now without playing unbelievable tennis for her.

"I think the rest of us are watching it thinking, 'wow, this is incredible', but when you watch her, she seems completely in control of all of it."

Australian Associated Press