Pegula, in search of the first title of her career on clay (green), will have to face the Swiss, 11th in the world, already titled in Adelaide and Abu Dhabi, this season.
The logic is respected in North Carolina since the first four seeds of this tournament 500 have reached the last square.
In the second semifinal, Tunisia's Ons Jabeur, who took advantage of Anna Kalinskaya's forfeit in the quarters, will face another Russian, Daria Kasatkina, who beat Madison Keys, 6-7 (5/7), 6-4, 6-2.
Jabeur, a former world No. 2, will play her second semi-final this season, after Adelaide in January. Since then, the Wimbledon and US Open finalist last year has undergone surgery after injuring her knee at the Australian Open.
She missed the WTA tournaments in Doha and Dubai and, after falling in the third round at Indian Wells, lost her first round in Miami.
The world No. 5 seems to be back in form from last year. In Charleston, she has yet to concede a set.
© 2023 AFP