Zhuhai – Julia Goerges beat top seed Kristina Mladenovic 6-2, 7-6 (7/4) to reach the WTA Elite Trophy semi-finals and send the Frenchwoman tumbling out of the world top 10 on Friday.
The number seven seed joins American CoCo Vandeweghe, Australia's Ashleigh Barty, and Anastasija Sevastova of Latvia in the race to the final in Zhuhai, southern China.
Mladenovic needed a straight-sets win to reach the semis but instead went down in one hour, 36 minutes, ceding her number 10 ranking to America's CoCo Vandeweghe.
It ends a career-high season for Mladenovic, now world number 11.
She finished 2016 ranked 42nd but won her first tour title in St Petersburg and reached three other finals this year.
Later China's number one player Peng Shuai downed Elena Vesnina 6-2, 1-0 after the Russian was forced to retire due to injury.
But despite her win, the round robin format of the tournament means Peng, a wildcard entry making her debut in Zhuhai, will not go through to the semis.
The 25-year-old, the oldest player in the tournament, lost to Vandeweghe earlier in the week.Let's (Why?)