Roberta Vinci was one of five seeds dumped out of the Nurnberger Versicherungscup in a day of upsets on Wednesday.
Top seed Vinci looked to be in good form having raced into a 3-0 lead against qualifier Kiki Bertens in their second-round contest, however the Dutchwoman reeled off five games in a row to take the opening set.
The second was much tighter but Vinci lost her nerve in the breaker, Bertens converting her first match point to complete a 6-4 7-6 (7-4) win.
Bertens will face Irina Falconi in the quarter-finals after she sent sixth seed Misaki Doi tumbling out 6-3 5-7 6-4.
Sabine Lisicki's problems on clay continued as she was beaten 6-2 7-6 (7-5) by world number 69 Varvara Lepchenko.
The former Wimbledon finalist - and fifth seed - has now lost four of her seven matches on clay this season, failing to get past the second round in all five tournaments she has played.
Yulia Putintseva also bowed out on Wednesday as she was beaten 6-4 6-2 by Julia Goerges, while second seed Laura Siegemund made it a clean sweep of exits on Wednesday.
Siegemund - who reached the final in Stuttgart last month - battled back after losing the first set to Mariana Duque-Marino, but she could not complete the comeback as the Colombian earned a 7-6 (8-6) 3-6 6-1 victory.