Mladenovic teamed with Hungary's Timea Babos on Saturday to beat Barty and German Julia Goerges 7-5 6-4 in the second round.

Barty and Goerges blew a 4-0 lead in the first set as Mladenovic returned to haunt Australia's all-conquering world No.1.

Mladenovic upset the French Open champion in last year's Fed Cup final, before powering France to the title with another victory with Caroline Garcia over Barty and Samantha Stosur in the deciding doubles rubber in Perth.

Her doubles exit, though, might prove a blessing as Barty continues her quest to become Australia's first Open singles champion since Chris O'Neil in 1978.

The top seed faces an intriguing fourth-round return bout against Alison Riske on Sunday after the American had eliminated Barty last year at Wimbledon.

"Obviously, it was a great memory for me. It was my first career (grand slam) quarter-final after winning that," Riske said.

"It was a really special match for me. I played my game, I looked to impose myself on her and it was good enough that day."

Riske has climbed from 55th to No.19 in the world since stunningly snapping Barty's 15-match European winning streak that featured French Open glory and her ascent to world No.1 for the first time.

"It's going to be a different experience. I'm playing on her home turf. I expect the fans against me, as they should be," the underdog said.

"But, yeah, look, I'm going to have to ignore the crowd and try to be in my own head, so I think that will be the focus.

"I'm excited for it, honestly. It's a rare experience that, at a grand slam, you play someone necessarily from the home country.

"So I'm definitely looking forward to it and it's going to be a battle."

The winner will play seventh seed Petra Kvitova, in what would be a quarter-final rematch for Barty after losing to the Czech left-hander last year, or Greece's Maria Sakkari on Tuesday.

Australian Associated Press