Olympic gold medallist Belinda Bencic and defending champion Jelena Ostapenko both sealed their quarter-final places at the Luxembourg Open.
Amanda Anisimova was among those to advance on a day of comebacks in Charleston, while Saisai Zheng advanced at the Copa Colsanitas.
Zarina Diyas got the better of "legend" Venus Williams at the Miami Open, while there were wins for Shelby Rogers and Ajla Tomljanovic.