Venus Williams fought back from a set down to beat South Africa's Chanelle Scheepers 2-6 6-3 6-2 as the top seeds advanced with little trouble at the Cincinnati Tennis Open.
Williams will now meet Italian Sara Errani for a quarter-final berth following the seventh seed's 6-4 6-4 win over Slovakian Daniela Hantuchova.
Top seed Agnieszka Radwanska defeated Sweden's Sofia Arvidsson 6-4 6-3 to book her place in the third round and will next face American Sloane Stephens after she beat fellow wildcard Camila Giorgi of Italy 6-2 6-1 in an hour.
Her sister Urszula Radwanska, ranked 46th in the world, progressed to the third round after Kazakh Yaroslava Shvedova retired due to heat illness.
Denmark's world number eight Caroline Wozniacki needed just 59 minutes to dismiss Kazakh Sesil Karatantcheva 6-1 6-0 and will next play Russian Anastasia Pavlyuchenkova, who swept aside Germany's Julia Goerges 6-3 6-0.
