Second seed Aryna Sabalenka suffered a shock exit at the Adelaide International on Wednesday after a 7-6(6) 6-1 defeat to world number 100 Kaja Juvan of Slovenia in the second round, while Shelby Rogers stunned Maria Sakkari 7-6(5) 2-6 6-4.
World number two Sabalenka, a semi-finalist at last year's Wimbledon and U.S. Open, struggled with her serve, racking up 18 double faults, and committed 49 unforced errors in the shock loss to the 21-year-old at the Australian Open warm-up event.
Juvan won a tight first set after trailing 2-0 and saved a set point at 6-5 in the tiebreak, before racing ahead 3-0 in the second to storm to victory in an hour and a half.
"I really enjoyed the first set. I love when matches get tight, when it's competitive and when it's a really tight fight," Juvan said after sealing her place in the quarter-finals.
"I was feeling a little bit sorry at some points because I ... knew she's not doing the best with the serve and we all know how that feels at one point. I know she can do it better."
Rogers beat Sakkari in straight sets in the second round at Wimbledon last year and looked on course for a repeat in Adelaide but lost seven straight games after being 2-0 up in the second set.
{{/usCountry}}Rogers beat Sakkari in straight sets in the second round at Wimbledon last year and looked on course for a repeat in Adelaide but lost seven straight games after being 2-0 up in the second set.
{{/usCountry}}World number six Sakkari forced the decider but Shelby fought her way back to close out the win in two hours and 18 minutes.
"It's nice to start with a big win like that. I knew it was going to be really tough today," Rogers said.
"She's coming off an incredible season last year and she's such a great competitor, so I knew I had to bring my best tennis, whatever that looks like at the beginning of the year."
Rogers will next take on seventh seed Elena Rybakina, who secured a 6-3 6-4 win over Czech qualifier Marie Bouzkova.
World number one Ash Barty will face American Coco Gauff later on Wednesday.