Angelique Kerber upset top seed Maria Sharapova in the quarter-finals of the Open GDF Suez in Paris, while Julia Goerges was also a shock loser.
Kerber, seeded ninth for the tournament, stunned Australian Open finalist Sharapova 6-4 6-4 in 90 minutes on Friday (local time) to book her spot in the semi-finals.
The players dropped their serve in the first set, but Kerber's impressive first serve percentage of 83 helped consolidate a late break to claim the opener 6-4.
It was a similar story in the second set as Kerber again took a late break and served out the match, setting up a last-four showdown with Yanina Wickmayer.
The Belgian survived a tough fight against rising star Mona Barthel, eventually winning 6-4 6-7 (3-7) 6-3.
It looked like the world No.29 was on track for victory after claiming the first set, but Barthel, who beat Wickmayer in the final of the Hobart International last month, would not lie down and raced to a 5-1 lead in the second.
Wickmayer clawed her was back to 5-5, only for Barthel to respond and win the set in a tie-breaker, forcing the match into a deciding set.
There, Wickmayer's experience shone through, claiming the decisive break and serving out the match at the first opportunity.
Czech Klara Zakopalova also progressed to the last four after she came from a set down to beat sixth seed Goerges 3-6 7-5 6-1 in just over two hours.
The world No.51 looked shaky early as Goerges claimed the only break of the first set, but slowly improved as the match wore on to square her career head-to-head with the German at 2-2.
She will now face France's Marion Bartoli in the semi-finals after the second seed edged past Roberta Vinci 4-6 6-4 7-6 (7-2).
Little separated the pair throughout the match, but Bartoli came up with the big shots when it mattered in the third-set tie-breaker to claim the win.
Meanwhile, Romanian Sorana Cirstea advanced to the semi-finals of the Pattaya Open in Thailand after Vera Zvonareva withdrew with a hip injury.
Scores were poised at 6-2 4-6 2-2 when the top-seeded Russian was forced to retire hurt from their quarter-final clash.
"I rushed too much in the first set. Then I tried to be more patient and made her play more, while my serves and returns were better in the second set," Cirstea, the seventh seed, said.
"However, I didn't notice that she was injured and was surprised she retired. I hope she will recover soon."
The 21-year-old will now face fourth seed Maria Kirilenko in the last four after she accounted for local hope Tamarine Tanasugarn 7-6 (7-2) 6-1.
Defending champion Daniela Hantuchova from Slovakia is also through to the semis after defeating American eighth seed Vania King 7-6 (9-7) 6-4.
The third seed was made to work hard for her win, but now has a great chance to claim the title for a second year running as the highest seed left in the draw.
Hantuchova will take on Taiwanese qualifier Hsieh Su-wei after she beat India's Sania Mirza 7-5 6-3.