Beijing - Unseeded Latvian Anastasija Sevastova stunned US Open champion Naomi Osaka 6-4, 6-4 to reach the China Open final on Saturday.
Sevastova, who dashed Osaka's hopes of reaching a third straight final, will face either Danish second seed Caroline Wozniacki or Chinese wildcard Wang Qiang on Sunday.
Osaka, 20, required treatment on her lower back midway through the second set. Last month she won her maiden Grand Slam title in a stormy final in New York, and was runner-up at the Pan Pacific Open in Tokyo.
The Japanese eighth seed, who beat a raging Serena Williams in the US Open final, had been on the verge of tears during her quarter-final victory over Zhang Shuai on Friday.
Sevastova, now ranked 20th in the world, was so sick of getting injured - she had particular problems with her back - that she quit tennis in May 2013 and studied leisure management.
The time off allowed her body to mend and she returned to the sport in January 2015.
The 28-year-old is now just one victory away from her fourth - but biggest - WTA title of her career in Beijing.