No.26 Emma Navarro advanced to her third quarterfinal of the season after defeating Katerina Siniakova 6-3, 3-6, 6-1 at the Cymbiotika San Diego Open. The victory is Navarro's second over Siniakova this month, having bested the Czech in three sets at the Dubai Duty Free Tennis Championships. 

Navarro will face Australian qualifier Daria Saville on Friday. She is bidding to make her third semifinal of the season and first at a WTA 500 since San Diego last fall. The 22-year-old from Charleston 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). 

Seeded No.3 in San Diego, Navarro improved her head-to-head over Siniakova to 2-1 with a gritty serving performance. While Siniakova outgunned her from the baseline, striking 23 winners to Navarro's 15, the American proved difficult to break. 

Siniakova generated nine break point chances but Navarro saved six of them. In contrast, Navarro converted five of her seven break chances. 

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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. World No.28 Vekic is now into her second quarterfinal of the season, following her semifinal showing at Linz a month ago.

"It was a very tough match today, tough conditions, and she played really well," Vekic said afterwards. "Really happy to win today and have another opportunity tomorrow."

Stakusic, who broke through last year as one of the heroines in Canada's run to their maiden Billie Jean King Cup championship, slammed a winning volley to go up a break in the third set at 2-1.

But former Top 20 player Vekic refused to yield in the decider and quickly broke Stakusic twice in succession, moving ahead 4-2 and claiming the break lead for herself. Vekic coolly served out the match at 5-3, finishing the encounter with a 76 percent success rate behind her first serve.

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

Anna Blinkova also moved into the quarterfinals with a win on Thursday. Blinkova, who defeated former World No.1 Caroline Wozniacki on Tuesday, backed up that victory with a 7-6(6), 6-2 win over No.5 seed and 2024 Australian Open semifinalist Dayana Yastremska.

Blinkova will meet No.1 seed Jessica Pegula on Friday. Pegula has won her two prior meetings with Blinkova, which both took place in 2023.

Anastasia Pavlyuchenkova closed out the night with a remarkable comeback victory. Pavlyuchenkova was down 6-4, 4-0 before storming back to defeat Wang Xinyu 4-6, 7-6(5), 6-2. Pavlyuchenkova will face No.6 seed Marta Kostyuk in the quarterfinals.