World No.2 Karolina Pliskova, fifth-ranked Elina Svitolina and sixth seed Belinda Bencic all joined 2019 champion Naomi Osaka and seven-time winner Serena Willams on the Open scrap heap with shock third-round exits.

Elevated to outright favourite to break Australia's 42-year Open title drought, Barty's highest-ranked obstacle in her path to the final is world No.7 Petra Kvitova, while the bottom half of the draw has also been blown wide open.

Russian Anastasia Pavlyuchenkova snapped a run of six-straight defeats to Pliskova to end the big-serving Czech's campaign with a shock 7-6 (7-4) 7-6 (7-3) win on Rod Laver Arena in the day's first big upset.

Pliskova was previously unbeaten in 2020, having won the season-opening Brisbane International and two earlier matches in Melbourne.

But the second seed never looked comfortable in Saturday's warmer conditions, throwing her racquet in disgust at one changeover and generally labouring about the court throughout the two-hour, 25-minute encounter.

"Let's say I was about 40 per cent today," Pliskova said.

Twice previously a quarter-finalist in Melbourne, including last year, Pavlyuchenkova's victory was her 33rd over a top-10 rival - but her first against Pliskova.

"I am really happy," the tournament's 30th seed said.

"I know we always say we want to enjoy, but I did enjoy. I had goosebumps after some points.

"It was really nice to get a win and beat Karolina for the first time - it was amazing.

"Honestly, I was trying to think 'OK, if I take at least one or two games on her serve, it would be amazing', because she serves so good.

"She is the ace queen on tour. That was my goal - to return well today."

Pavlyuchenkova moves on to play Angelique Kerber for a quarter-final spot.

Germany's 2016 champion and former world No.1 continued her quiet progression through the draw with a hard-fought 6-2 6-7 (4-7) 6-3 win over Italian Camila Giorgi.

Bencic bombed out in a 6-0 6-1 capitulation to Estonia's Anett Kontaveit before former world No.1 Garbine Muguruza sent Svitolina packing with a 6-1 6-2, 67-minute dispatch of the 2019 WTA Finals runner-up.

Eyeing her first grand slam quarter-final, Kontaveit faces Iga Swiatek on Monday, with the unheralded Pole ousting Croatian 19th seed Donna Vekic 7-5 6-3.

The resurgent Muguruza plays ninth seed Kiki Bertens or Zarina Diyas next on Monday for a quarter-final spot.

Wimbledon champion Simona Halep avoided the exodus of big-name stars with a stress-free 6-1 6-4 win on Saturday over Yulia Putintseva to emerge as the finals favourite from the depleted bottom half.

The fourth seed and 2018 runner-up will play Elise Mertens after Belgium's 16th seed and 2018 semi-finalist stopped American CiCi Bellis 6-1 6-7 (5-7) 6-0.

Australian Associated Press