Petra Kvitova remains on course to win her fourth Connecticut Open title after getting past Zarina Diyas in three sets on Wednesday.
Czech Kvitova, seeded third for the WTA Premier event in New Haven, overcame her Kazakh opponent 6-1 5-7 6-2 to book a meeting with Carla Suarez Navarro in the quarter-finals, as the world number five seeks to add to the titles she won in 2012, 2014 and 2015.
Aryna Sabalenka surprised defending champion Daria Gavrilova, beating the ninth seed 6-3 6-7 (6-8) 7-5 to advance to a last-eight match against Belinda Bencic.
Ekaterina Makarova also won in three sets, the Russian overcoming Slovakian Magdalena Rybarikova, the 2014 beaten finalist, 2-6 6-3 6-3. She will face fifth seed Julia Goerges in the quarter-finals.
Monica Puig eased to a straight-sets win over Anett Kontaveit, with second seed Caroline Garcia her next opponent.