Petra Kvitova has dismissed Poland's Agnieszka Radwanska in her bid for a fourth Connecticut Open title.
The two-time Wimbledon champion, who has won three times before in New Haven, prevailed 6-1, 7-6 (7/3) to reach the second round.
While Kvitova put in a clinical performance in the first set, breaking her opponent twice, she faced a tougher challenge in the second.
The Czech clawed her way back from 3-1 down to force a narrow tie-break and advance after almost one and a half hours on court.
The No.3 seed will now face Zarina Diyas, who defeated Maria Sakkari 6-4, 6-3.
Great Britain's Johanna Konta made the last 16 by beating Laura Siegemund 6-2, 7-5.
Konta had lost her two previous meetings to the German, but she raced to a 4-0 lead and closed out the first set with her fourth ace.
Siegemund, who spent 10 months out of the game after tearing a cruciate ligament in her knee in May 2017, fought back in the second set and a tie-break looked on the cards at 5-5.
But successive double faults from Siegemund allowed Konta to serve out and set up a last-16 meeting with Spain's Carla Suarez Navarro.
Meanwhile, Ekaterina Makarova dismissed No.4 seed Karolina Pliskova 6-1, 6-3 in 58 minutes.
Up next for Makarova is 2017 Wimbledon semi-finalist Magdalena Rybarikova, who progressed after CoCo Vandeweghe retired injured in the third set.
Aliaksandra Sasnovich, of Belarus, overcame France's Kristina Mladenovic 7-6 (8/6), 6-7 (3/7), 6-2 to book a last-16 date with No.2 seed Caroline Garcia, and Ukraine's Dayana Yastremska defeated American Danielle Collins 6-0, 6-3 to face Julia Goerges.
Earlier, world No.1 Simona Halep announced her withdrawal from the tournament, citing an injury to her right Achilles.
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