The win is Navarro's second over Siniakova this month, having bested the Czech in three sets at the Dubai Tennis Championships.

Navarro will face Australian qualifier Daria Saville on Friday in a bid to make her third semifinal of the season and first at a WTA 500 since San Diego last fall.

The 22-year-old won her first WTA title in January in Hobart and has already notched 14 main draw wins this season. She is tied with World No.1 Iga Swiatek for the third-most wins this season, sitting behind only Elena Rybakina (17) and Jelena Ostapenko (16), according to ATP.

Earlier in the day, No.7 seed Donna Vekic of Croatia fended off a valiant effort by Canadian teenager Marina Stakusic before posting a 6-4, 3-6, 6-3 win to reach the quarterfinals.

Vekic, the 2022 San Diego runner-up, took exactly 2 hours to overcome rising 19-year-old Stakusic, a qualifier ranked No.283 and paved the way into her second quarterfinal of the season, following her semifinal showing at Linz a month ago.

She will face Great Britain's Katie Boulter in the quarterfinals. It will be the first meeting between Vekic and 49th-ranked Boulter, who upset No.2 seed Beatriz Haddad Maia on Wednesday.