Misaki Doi and Anna-Lena Friedsam will meet in the San Antonio Open final after last-four victories on Friday.
Japanese sixth seed Doi battled past Tsvetana Pironkova, completing a 6-4 2-6 6-4 win on the hard courts at the WTA 125K series event.
Doi broke three times in the third set to close out victory in two hours 15 minutes.
With her win, Doi reached a third WTA Tour final and second of the year as she looks to add to her 2015 Luxembourg Open crown.
Friedsam had it much easier, overcoming Alison Riske 6-3 7-6 (7-4).
The German sent down six aces in her triumph, progressing to a third final on the WTA Tour and also seeking a second title.