Kerber defeated Patricia Mayr-Achleitner 6-3, 6-1 in a brisk 54 minutes. Kerber lost only 11 points over eight games serving and converted four of her seven break chances.
That gave her a spot in Saturday's tournament semifinals but also locked in an invitation to the season-ending WTA Championships.
Stefanie Voegele eliminated second-seeded Sloane Stephens 6-7 (3-7), 6-4, 7-5 in a match that took nearly 3 hours. Stephens won a seesaw first set in which both players had their serves broken three times but Voegele had the only break of the second set and advanced with two more in the third.
Carla Suarez Navarro, the fourth seed, claimed her spot in the semis with a 6-1, 6-3 decision over fifth-seeded Kirsten Flipkens, saving the only break point she faced.
Kerber will go against Suarez Navarro in the semifinals. Suarez Navarro won a three-set decision over Kerber in the fourth round of the 2013 U.S. Open in their only previous match. Ivanovic plays Voegele in the other semi. It is their first match against each other.
Kerber's win set the invitation list for the Oct. 22-27 WTA Championships. The other players to be invited to the eight-player event are Serena Williams, Victoria Azarenka, Agnieszka Radwanska, Li Na, Petra Kvitova, Sara Errani and Jelena Jankovic.
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