Kiki Bertens remains on course for a hat-trick of Nuremberg Cup titles after overcoming Mona Barthel in three sets to reach the quarter-finals.
Dutch third seed Bertens, tournament winner in 2016 and 2017, hit back from a set down to beat Germany's Barthel 6-7 (2/7) 6-2 6-4.
Bertens faces a last-eight clash with Belgium's Kirsten Flipkens, while American Alison Riske will play Sorana Cirstea of Romania in the other outstanding quarter-final.
Johanna Larsson overcame Kristyna Pliskova in three tough sets to reach the semi-finals.
Unseeded Swede Larsson recovered from a set down to beat Czech Republic's Pliskova 5-7 7-5 6-4 in over two and a quarter hours and will play Katerina Siniakova in the last four.
Number eight seed Siniakova won through two matches on Thursday, completing a 7-5 6-4 win against Paraguay's Veronica Cepede Royg before defeating teenage qualifier Fanny Stollar, who knocked out Britain's Heather Watson in the previous round, 7-5 6-4.
At the Internationaux de Strasbourg, top seeded Australian Ashleigh Barty reached the semi-finals with a 7-5 6-4 win against China's Qiang Wang.
Barty, 22, will bid to reach the first final of her career on clay against Russian third seed Anastasia Pavlyuchenkova, who beat Kazakhstan's Zarina Diyas 6-4 6-2.
Slovakia's Dominika Cibulkova will meet Romanian Mihaela Buzarnescu in the other semi-final.
World number four Cibulkova came through against Samantha Stosur 6-4 6-3, while fourth seed Buzarnescu breezed past Taiwan's Hsieh Su-Wei 6-0 6-3.