The 49th-ranked Karolina Muchova stunned top seed Aryna Sabalenka in three sets to reach the China Open semi-finals on Friday.
The Czech player won 7-6 (7/5), 2-6, 6-4 and faces China's Olympic champion Zheng Qinwen or 17-year-old Russian Mirra Andreeva for a place in the final.
Last year's US Open champion Coco Gauff plays Spain's former world number two Paula Badosa in the other semi-final in Beijing.
World number two Sabalenka was on a streak of 15 victories in a row, claiming titles in Cincinnati and then the US Open for the first time.
The Belarusian previously had trouble though with Muchova, who this time last year was inside the top 10 before injury struck.
US Open semi-finalist Muchova had won the last two meetings between them with both going to a deciding set.
This encounter proved to be just as tight.
Three-time major champion Sabalenka faced three break points at the start but she held firm, then had a sniff herself on her opponent's serve at 2-1, but Muchova similarly refused to buckle.
The hard-hitting Sabalenka had set point on Muchova's serve at 5-4 but surrendered the opportunity when she rattled her forehand wide on the Czech's second serve.
Muchova double-faulted to give Sabalenka another chance to wrap up the set but again she failed to take it.
The Czech had two set points in the tiebreak and grabbed the second at the end of a thrilling rally to go a set up.
It was the first set 26-year-old Sabalenka had dropped since the third round in New York.
Sabalenka started the second set brightly to break for 2-1 and broke once more on the way to sealing the set with comparative ease.
Neither could hold serve in the deciding set before Muchova, who at one point had appeared to be wilting in the face of her opponent's superior power, clinched the match in two hours, 46 minutes.
This time last year 28-year-old Muchova was ranked ninth in the world having reached the French Open final and semi-finals at Flushing Meadows.
But her 2023 season ended after the US Open because of wrist surgery and she did not play for nearly 10 months until returning this summer.
AFP