Garbine Muguruza had to struggle two days after ending the current comeback of Kim Clijsters as Spain's double grand Slam champion grappled with her world number 39 opponent.
Elina Svitolina became the latest seed in the women's draw to make an exit after being well beaten by unseeded Garbine Muguruza in the third round.
Karolina Pliskova's defeat to Anastasia Pavlyuchenkova means that two of the top three seeds are now out of the women's draw at the Australian Open.
World number two Karolina Pliskova barrelled into the Australian Open second round on Tuesday as she chases her first Grand Slam crown.
Dumped out of the Brisbane International last week, Ashleigh Barty retains a comfortable cushion of 1,607 points over Karolina Pliskova, who went on to win the Brisbane title.
Karolina Pliskova's third Brisbane International title in four years and her 16th on the WTA tour, stamps her as one of the favourites for the Australian Open.
Karolina Pliskova triumphed 6-7 (10/12), 7-6 (7/3), 6-2 in a two hour, 48 minute marathon and will play eighth seed American Madison Keys in the decider.
Karolina Pliskova has hired Venezuelan coach Daniel Vallverdu with former Ukraine Fed Cup player Olga Savchuk -- a long-time friend -- also joining her team.
Ashleigh Barty won four titles in 2019 including the prestigious WTA Finals and finished the year on top of the WTA rankings.
Ashleigh Barty, playing in her WTA Finals debut, will look to cap off a momentous season when she plays Elina Svitolina in Sunday's final.
World No.12 Sofia Kenin replaced Bianca Andreescu after the US Open champion suffered a knee injury against Karolina Pliskova on Wednesday.
WTA Finals: Simona Halep moved on top of Purple Group alongside defending champion Elina Svitolina who earlier beat No.2 seed Karolina Pliskova.
WTA Rankings: Ashleigh Barty once again retained the top spot in but will have to produce her top performance at Wuhan Open to retain her No. 1 spot.
Karolina Pliskova struggled into the second round of the US Open on Monday while 2014 runner-up Kei Nishikori of Japan needed only 47 minutes to advance.
Naomi Osaka benefitted from the second round defeat of former number one Ashleigh Barty and the failure of Karolina Pliskova to reach the semis in Toronto.
Roger Federer is the oldest man to book a last-16 place since Tunisian-born Italian Nicola Pietrangeli, a two-time champion, at the age of 38 in 1972.
Serena Williams heads into this year's French Open with questions surrounding her fitness while Naomi Osaka needs to rediscover her best form to solidify her position at the top of the women's game.
Ashleigh Barty will rise from 11th to number nine in the world rankings and become the first Australian woman since Sam Stosur in June 2013 to crack the top 10.