Mihaela Buzarnescu dumped Elina Svitolina out of the Birmingham Classic, while top seed Caroline Garcia was beaten at the Mallorca Open on Friday.
Svitolina was the highest ranked player in the quarter-final draw in Birmingham, with Garbine Muguruza knocked out earlier in the week, but she too fell by the wayside.
Buzarnescu defeated Svitolina at the French Open and she came out on top in a second meeting in a matter of weeks, triumphing 6-3 6-2.
"I didn't go on the court thinking I played her three weeks ago," Buzarnescu said. "She's an amazing player, so young and so many achievements until now and so many to come.
"I just tried to go on the court, play my own game and focus on each point and take it as an ordinary match."
Buzarnescu moves into her first WTA Premier-level semi-final, where she will face defending champion Petra Kvitova, who breezed past Julia Goerges 6-1 6-4.
Barbora Strycova and Magdalena Rybarikova make up the last-four draw, Lesia Tsurenko's retirement handing the former victory while Dalila Jakupovic lost to the latter.
In Mallorca, Garcia went down 6-3 6-3 to Sofia Kenin, with Lucie Safarova, another seed, also knocked out by Tatjana Maria.
Teenager Kenin will now play the first WTA Tour semi-final of her career.
"I'm very happy. [Garcia] is a great player," she said. "It was a really tough match and I knew I had to fight until the end."
Alison Riske was defeated by Sam Stosur, and third seed Anastasija Sevastova came from behind to get past Ajla Tomljanovic 3-6 6-3 6-1.