Italian Flavia Pennetta caused an upset by beating third seed Jelena Jankovic 2-6, 6-4, 6-4 in the Stuttgart Grand Prix quarter-finals on Friday.
The unseeded Pennetta's reward is a last-four meeting with Dinara Safina after the world number one swept aside Pole Agnieszka Radwanska 6-4, 6-2.
Russian Safina, who went to the top of the rankings last week, dominated the eighth seed with a series of thunderous groundstrokes.
Second seed Elena Dementieva went through with a 6-2, 4-6, 6-3 victory over Marion Bartoli of France.
The Russian next meets countrywoman Svetlana Kuznetsova after the fifth seed overwhelmed Argentine Gisela Dulko 6-3, 6-2.
Dementieva and Bartoli traded early breaks before the world number three started going to the net more often as she clinched the first set in 31 minutes.
Bartoli produced some deft baseline play to break serve twice in the second.
However, there was no looking back for Dementieva after she raced into a 4-0 lead in the deciding set.
