Karolina Pliskova became the latest high-profile casualty at the Australian Open, the second seed stunned by Anastasia Pavlyuchenkova in straight sets.
Defending champion Naomi Osaka and 23-time grand slam winner Serena Williams crashed out at Melbourne Park on Friday.
Pliskova – another women's singles contender – joined the star duo in departing the year's opening slam following Saturday's 7-6 (7-4) 7-6 (7-3) defeat to 30th seed and two-time quarter-finalist Pavlyuchenkova.
A semi-finalist last year, Pliskova had matched or improved her best results at the Australian Open year-on-year since debuting in 2013.
However, the 2016 US Open runner-up was unable to build on her performances at Melbourne Park, where she succumbed to the aggressive Pavlyuchenkova in a gruelling encounter on Rod Laver Arena.
Pavlyuchenkova raced out to a 4-1 lead in the opening set, which was highlighted by a 30-point second game, before eventually prevailing in a tie-break after Pliskova rallied.
Pliskova, who finished with 35 winners and 29 unforced errors, recovered from a slow start in the second to force another tie-break but the Czech star was unable to send the match into a deciding set.
After tallying 51 winners and 43 unforced errors in two hours, 25 minutes, Pavlyuchenkova will face 2016 champion and three-time slam winner Angelique Kerber in the last 16.