Top seed Petra Kvitova highlighted Wednesday's winners at the inaugural Katowice Open.
The world No. 8 former Wimbledon champion got past Japan's Misaki Doi 6-4, 6-4 in a first-round match on the indoor surface at Spodek.
Kvitova was joined in the second round by second-seeded Italian Roberta Vinci, a 6-2, 2-0, retired winner against Czech Andrea Hlavackova on Day 3.
In some second-round play, Italian qualifier Maria Elena Camerin bounced third-seeded Czech Klara Zakopalova 7-5, 3-6, 6-3 and Czech wild card Karolina Pliskova upended on-the-mend Estonian Kaia Kanepi 7-5, 6-3. The sixth-seeded Kanepi returned this week after a lengthy absence caused by an Achilles injury.
A first-round upset came when Romanian qualifier Alexandra Cadantu dismissed seventh-seeded German slugger Sabine Lisicki 7-5, 6-2.
In some additional second-round play, Croat Petra Martic handled Slovakian qualifier Anna Schmiedlova 6-4, 6-2 and German Annika Beck overcame Spaniard Lourdes Dominguez Lino 5-7, 6-3, 6-2. Beck will face Camerin in a quarterfinal on Friday.
Kvitova will encounter Luxembourg's Mandy Minella and Vinci will battle Dutchwoman Kiki Bertens in a pair of second-round affairs on Thursday.