Jessica Pegula admitted Tuesday she felt "helpless" against ruthless world number one Ashleigh Barty, saying she "plays more like a guy".

The American 21st seed had beaten powerful fifth seed Maria Sakkari to make the last eight at Melbourne Park for the second straight year.

But she was no match for the unrelenting Australian who crushed her 6-2, 6-0 in just 63 minutes on Rod Laver Arena.

Pegula said Barty is so good she was "living in everyone's head a little bit".

"You feel pretty helpless," she said. 

"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."

Barty has lost just 17 games in five matches to reach her fourth Grand Slam semi-final as she targets a first title on home soil.

Since her last semi-final appearance at Melbourne Park in 2020, when she was upset by eventual champion Sofia Kenin, she has been dominant, reigning as world number one for 112 consecutive weeks.

Pegula said it was incredibly hard to figure out her game.

"Honestly, she just does everything I think a little bit better than everybody," she said.

"She kind of plays more like a guy, maybe a different kind of style that we're not used to playing day-in and day-out. 

"So it's really hard to come from someone that hits the ball really hard to someone that's giving you all these different shots that you don't normally see.

"I think she's definitely living in everyone's head a little bit."