Third seed Polona Hercog was an early casualty at the Tashkent Open in Uzbekistan as she was dumped out of the first round by Aliaksandra Sasnovich.
Slovenian Hercog looked on course for a routine victory when she took the first set but 21-year-old Belarusian Sasnovich fought back to claim a 4-6 6-3 6-3 win in just over two hours.
Hercog was not the only seed to tumble out either, as number seven Jelena Ostapenko suffered a 4-6 6-2 7-5 loss to Bojana Jovanovski, while eighth seed Andreea Mitu was beaten 7-5 6-3 by Yaroslava Shvedova.
Top seed Annika Beck had fewer troubles as she sealed her place in the second round with a 6-3 6-1 triumph over Elizaveta Kulichkova, although the German did not have things all her own way.
The world number 43 had to save five break points in each set before booking a meeting with Jana Cepelova, who enjoyed a comfortable 6-2 6-1 win over wildcard Sabina Sharipova.
Fourth seed Johanna Larsson and Katerina Siniakova, seeded fifth, enjoyed 6-3 6-3 and 6-2 7-6 (7/5) victories over Stefanie Voegele and Paula Kania respectively.
Aleksandra Krunic beat Anett Kontaveit 6-2 6-4, Evgeniya Rodina was a 6-2 6-4 victor against Urszula Radwanska and Donna Vekic survived a scare to secure a 6-3 1-6 6-3 victory over Kiki Bertens.
In Tuesday's other first-round ties, Klara Koukalova eased to a 6-4 6-0 triumph against Kateryna Kozlova and Nigina Abduraimova defeated Petra Martic by the same scoreline.