Beatriz Haddad Maia sprung a surprise on Bol Open top seed Johanna Larsson with a straight-sets second-round win on Thursday.
The Brazilian triumphed 7-6 (7-3) 6-1 in Croatia, ending Larsson's run in the week after she was knocked out of the French Open at the same stage.
Haddad Maia, ranked 101 in the world, will now face fifth seed Sara Errani following her 7-5 6-3 victory over Olga Saez Larra.
Second seed Mindy Minella continued her serene progress with a 6-2 7-6 (8-6) defeat of Chuang Chia-jung.
Also in the second round, Alexandra Cadantu beat Tereza Mrdeza in three sets, Aleksandra Krunic overcame Olga Govortsova, and Lina Gjorcheska lost to Ivana Jorovic.
The final match saw sixth seed Kateryna Bondarenko thrash Tena Lukas 6-0 6-2, while Maria Sakkari completes the quarter-final line-up after a walkover against Alison van Uytvanck.