American Emma Navarro, the No 3 seed, moved into the last four of the Bad Homburg Open when Dane wildcard Caroline Wozniacki retired.
Navarro, ranked No 19, led 4-6, 6-1, 1-0 when Wozniacki, ranked No 112, pulled out on Thursday at the Bod Hombourg vor der Höhe.
The American will face Russian Diana Shnaider next.
In the previous rounds of the Bad Hombourg tournament, Emma Navarro won against Romanian qualifier Jaqueline Cristian (6-3, 6-1) and Peyton Stearns (6-4, 6-1).
The 33-year-old Dane edged out Ukrainian Elina Svitolina, the No 7 seed (6-3, 6-7 (4), 7-5) and beat Russian Veronika Kudermetova (6-2, 6-4) earlier in the tournament.
Bad Homburg WTA 250, other quarter-finals results
