Top seed Dominika Cibulkova suffered a shock first round defeat to world number 161 Antonia Lottner at the Ricoh Open in s’Hertogenbosch.
The former Australian Open champion struggled on her serve throughout and her German opponent took full advantage to pull off a 7-5 2-6 6-4 upset win.
In second round action, seventh seed Lesia Tsurenko made it safely through with a 6-2 6-3 win over Petra Krejsova of the Czech Republic.
Germany’s Andrea Petkovic fell 6-3 5-7 6-2 to Natalia Vikhlyantseva, and there were also wins for Anett Kontaveit and Carina Witthoeft.
At the Aegon Open in Nottingham, American qualifier Kristie Ahn continued her impressive week with a 6-3 6-1 win over Magda Linette of Poland.
Former Wimbledon semi-finalist Tsvetana Pironkova also reached the quarter-finals as she overcame Kurumi Nara of Japan 6-3 6-2.
Ashleigh Barty eased past Croatian qualifier Jana Fett 6-2 6-1 but another Croatian, Donna Vekic, was a 6-3 6-4 winner over Julia Boserup of the USA.