Camila Giorgi charged into the Citi Open semi-finals as Hsieh Su-wei became the final seed to fall on Friday.
Giorgi has put together a fine run in Washington and the Italian brushed past Zarina Diyas 6-3 6-2 in their quarter-final at the WTA International event.
The 27-year-old is into her first semi-final of the year after needing just 72 minutes to dispose of Diyas.
Awaiting Giorgi in the last four is American wildcard Caty McNally, who upset fourth seed Hsieh.
Hsieh, the last seed standing at the tournament, was well beaten by the 17-year-old, who claimed a 6-4 6-3 victory.
The other semi-final will be between qualifier Anna Kalinskaya and Jessica Pegula.
Kalinskaya overcame Kristina Mladenovic 6-4 4-6 6-2 and Pegula edged Lauren Davis 6-2 7-6 (7-2).