Jelena Ostapenko's poor start to the season continued as the French Open champion was beaten by Ekaterina Makarova in the first round of the Sydney International.
Kristyna Pliskova defeated Ostapenko in her first competitive match of the year at the Shenzhen Open and the Latvian - who beat Serena Williams in a recent Abu Dhabi exhibition match - suffered another setback ahead of the Australian Open, losing 7-6 (7-3) 6-1 to Makarova in searing heat on Sunday.
There were three double faults in Ostapenko's first service game and although the third seed's fighting qualities enabled her to break three times in the opening set, she paid the price for too many errors in the tie-break.
Makarova only avoided the qualifying stages when her fellow Russian Anastasia Pavlyuchenkova withdrew due to injury and she took advantage of being handed a first-round spot, breaking twice in a one-sided second set to advance.
World number 343 Ellen Perez is a surprise name in the second round after Kristina Mladenovic retired at 6-4 4-2 down on a scorching day.
Mladenovic called for treatment a handful of times in gruelling conditions and the fifth seed was unable to see out the match, Perez advancing in her homeland at just her second WTA tournament.
World number 11 Mladenovic tweeted: "43 degrees but probably 50 on court when started, I’m sorry to the fans. I think it’s 1st time in my career I retired a match..it says it all"
Elena Vesnina also made it through, beating Lara Arruabarrena 6-2 6-2.
Mihaela Buzarnescu claimed the scalp of Alize Cornet in the opening round of the Hobart International, toppling the 2016 champion and fourth seed 6-2 6-4.
Yulia Putintseva, Varvara Lepchenko and Beatriz Haddad Maia also made it into the second round on day one of the tournament.