Top seed Garbine Muguruza was forced to retire injured during her second-round match at the Brisbane International as Aleksandra Krunic advanced.
The 2017 Wimbledon champion suffered muscle cramps when she was 5-2 up in the third set with the first two sets shared and pulled out, setting Serbian Krunic up for a quarter-final clash with seventh seed Anastasija Sevastova, who beat Sorana Cirstea.
Top seed Caroline Wozniacki eased into the second round at the ASB Classic with a straight-sets victory over Madison Brengle on a day where three seeds fell.
The Danish two-time US Open finalist claimed a 6-3 6-0 win against her American opponent in just under an hour to set up a second-round tie with Petra Martic of Croatia in Auckland.
Fifth seed Lauren Davis, sixth seed Yulia Putintseva and seventh seed Mona Barthel all crashed out in straight-sets defeats to qualifying duo Sachia Vickery and Ysaline Bonaventure and Varvara Lepchenko respectively.
Czech third seed Barbora Strycova saw off Italian Sara Errani 6-4 6-7 (3/7) 6-4, while Polish fourth seed Agnieszka Radwanska recorded another hard-fought 6-2 4-6 6-2 win over B eatriz Haddad Maia of Brazil to progress.
Fifth seed Johanna Konta overcame a tough start to beat Ajla Tomljanovic and advance to the last eight in Brisbane.
For the second game running the British number one fought back from losing the first set, eventually triumphing 4-6 6-1 6-4.
Meanwhile, Maria Sharapova saw off Alison Riske with a 4-6 6-3 6-2 comeback victory in the second round of the Shenzhen Open where two seeds fell.
Number two seed Jelena Ostapenko was knocked out of the first round after a 6-1 6-4 defeat to Kristyna Pliskova after third seed Shuai Zhang suffered a 6-3 6-7 (5/7) 6-4 loss against Zarina Diyas in the second round.
Timea Babos, seeded eighth, eased through to the quarter-finals with a 6-2 6-1 win over Magda Linette.