Top seed Julia Goerges battled through to the last four of the Luxembourg Open, while Daria Kasatkina got the better of compatriot Anastasia Pavlyuchenkova at the Kremlin Cup.
Donna Vekic gave Goerges a tough test on Thursday as she took their quarter-final meeting to three sets before ultimately falling short 6-3 3-6 6-3.
The sixth seed squandered numerous break-point opportunities in the first set before dominating the second, but Goerges finally rallied and booked her place in the next round.
The German will face Eugenie Bouchard, who benefited from Andrea Petkovic's retirement at 4-6 4-0.
Dayana Yastremska will be pitted against Belinda Bencic in the other semi-final, the duo having defeated Margarita Gasparyan and Vera Lapko respectively.
In Moscow at the Kremlin Cup, Kasatkina beat the unseeded Pavlyuchenkova 6-4 6-3 in an all-Russian encounter. Johanna Konta is up next for Kasatkina after she edged past Aliaksandra Sasnovich.
Anett Kontaveit was the only seed defeated on Thursday as Ons Jabeur stormed to a 7-5 6-1 triumph, setting up a clash with Anastasija Sevastova.
Fifth seed Sevastova came from behind to send another Russian packing, winning 4-6 7-5 6-3 against Vera Zvonareva.