Australian Open runner-up Elena Rybakina has been handed a humbling defeat ahead of the year's first Grand Slam.
The world number three was beaten 6-3 6-3 by the unseeded Ekaterina Alexandrova in the Adelaide International quarter-finals on Thursday.
Kazakh Rybakina laid down a marker by beating Melbourne Park champion Aryna Sabalenka in Sunday's Brisbane final but was well off the pace against world number 21 Alexandrova as she sought a second win in their fourth meeting.
The top seed found herself 4-0 down following an error-prone start before clawing her way back with some fierce ball-striking, but the counter-punching Alexandrova held firm and broke again to clinch the opening set.
Rybakina, who meets Karolina Pliskova in her first clash at the January 14-28 Australian Open, fell behind even further in the next set and mounted another comeback before Alexandrova fought back from 0-40 down at 5-3 to clinch the win.
Up next for Alexandrova is former world number five Jelena Ostapenko, who continued to gain momentum for another tilt at a Grand Slam title with a 7-5 6-3 win over Marta Kostyuk.
Second seed Jessica Pegula overcame Anastasia Pavlyuchenkova 6-7(1) 7-5 6-4 to set up a clash with Daria Kasatkina.
In the men's draw, Jack Draper stunned top seed Tommy Paul 6-1 6-4 to book a semi-final against Alexander Bublik, who saved a match point to outlast Lorenzo Musetti 6-3 6-7(4) 7-5.
Last year's Australian Open quarter-finalist Sebastian Korda advanced with a 6-4 6-4 victory over local favourite Christopher O'Connell and meets Jiri Lehecka after the Czech toppled second seed Nicolas Jarry 6-4 7-5.
At the Auckland Classic, top seed Ben Shelton made his third tour-level semi-final with a 6-4 6-3 win over Roberto Carballes Baena and will play Taro Daniel next. Daniel dug deep for a 6-4 6-7(3) 6-3 win over Alexandre Muller.
A wrist issue forced second-seeded Briton Cameron Norrie out of his contest with Alejandro Tabilo, who faces Arthur Fils on Friday for a spot in the final.
Frenchman Fils won the first set against Daniel Altmaier and was up 1-0 in the next when his opponent retired with injury.
Elsewhere, top seed Elise Mertens reached the Hobart semi-finals with a 7-5 6-0 win over Arantxa Rus and will face Daria Saville after the Australian rallied past Zhu Lin 3-6 6-1 6-4.
Second seed Emma Navarro reached her second semi-final in as many weeks by getting past Viktoriya Tomova and plays Yuan Yue following the Chinese player's 7-5 7-6(4) win over Yulia Putintseva.