Tunisian wild card Ons Jabeur stunned top seed and defending champion Bojana Jovanovski in the second round of the Baku Cup on Wednesday.
The 204th-ranked Jabeur converted 6-of-14 break-point chances in a 6-2, 7-5 victory over Jovanovski, who committed seven double faults.
Second-seeded Donna Vekic of Croatia and fourth-seeded Romanian Alexandra Cadantu both reached the quarterfinals. Vekic had little trouble in a 6-1, 6-2 pasting of Ukrainian qualifier Tetyana Arefyeva, while Cadantu avoided a second-round upset by battling back to beat Luxembourg's Mandy Minella, 5-7, 6-1, 6-3.
Chanelle Scheepers was one of four players to post first-round victories on Day 3. The third-seeded South African rallied for a 3-6, 6-3, 6-4 win over Czech Andrea Hlavackova.
Other winners were Kazakhstan's Galina Voskoboeva and Ukrainians Elina Svitolina and qualifier Kateryna Kozlova.
Voskoboeva knocked off sixth-seeded Polona Hercog of Slovenia, 7-6 (9-7), 4-6, 6-3, the seventh-seeded Svitolina overcame Serbian Aleksandra Krunic, 6-3, 4-6, 6-2, and Kozlova earned a 6-2, 3-6, 6-4 triumph over Greece's Eleni Daniilidou.
This week's champion will receive a first prize of $40,000.