Kenin won her first singles title of 2019 on the hardcourts of Hobart, Australia in January, and added her second on grass in Mallorca in June.
Stosur, who won the U.S. Open in 2011, was looking to win her first WTA title since Strasbourg in 2017.
At the Toray Pan Pacific tournament, top-seeded and last year’s U.S. Open champion Naomi Osaka beat Elise Mertens 6-4, 6-1 to reach the final. She will play Anastasia Pavlyuchenkova, who defeated Angelique Kerber 6-3, 6-3.
At the Korea Open in Seoul, Yafan Wang beat Karolina Muchova 7-6 (5), 6-4 and will face fourth-seeded Magda Linette of Poland in the final. Linette beat second-seeded Ekaterina Alexandrova 7-6 (5), 7-6 (7).