World No. 1 Aryna Sabalenka was upset by Kazakhstan's Elena Rybakina 7-5, 6-2 in the quarterfinals of the China Open on Friday.
The top-seeded Belarusian was haunted by service problems throughout the match, committing eight double faults against Rybakina's one, and was broken four times by the fifth seed.
Rybakina fired 12 aces while Sabalenka only managed four.
In the semifinal, Rybakina will face Liudmila Samsonova of Russia, who beat Latvia's Jelena Ostapenko 6-3, 6-2.
World No. 2 Iga Swiatek of Poland and world No. 3 Coco Gauff of the United States will square off in the other semifinal.
In the quarterfinals on Friday, Swiatek rallied from one set down to beat Caroline Garcia of France 6-7 (8), 7-6 (5), 6-1, while Gauff eased past Maria Sakkari of Greece 6-2, 6-4, extending her winning streak to 16 matches.