The Australian, the 2011 US Open champion, hit back to see off Viktorija Golubic 2-6 7-6 (7-4) 6-1 on Saturday (AEST) and advanced to her first title match since Strasbourg in 2017.
"I just tried to hang in there and find a way to start playing a bit better," Stosur, who will return next week to the world's top 100 as a result of her run in China, said.
"She's very tough to play against so I'm just happy to get through.
"This is where everyone wants to be, so to now make it to the final, I'm really happy and I'll give it my best shot on Saturday."
No.3 seed Kenin, from the United States, also required three sets to battle past Anna Blinkova 7-6 (7-2) 4-6 6-1.
In Seoul, No.2 seed Ekaterina Alexandrova overcame being a break down in the deciding set to beat Kristie Ahn 6-7 (0-7) 6-4 6-4.
The big-serving Russian, who fired down 22 aces, will meet fourth seed Magda Linette in the semi-finals. Linette was an impressive 6-2 6-3 victor over Kirsten Flipkens.
The other last-four clash pits Karolina Muchova against Wang Yafan.
Muchova beat Priscilla Hon 6-3 6-3 while Wang dropped just four games in easing past Paula Badosa.