Ohio - 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 Open on Wednesday.
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.
For the second successive day Williams needed three sets but she was glad with the way she recovered from a rusty opening
"I made so many errors. She's one of those players that puts a lot of balls in the court, makes you play a lot of shots and I wasn't getting them in the court. It was good to turn it around," said Williams.
Top seed Agnieszka Radwanska defeated Sweden's Sofia Arvidsson 6-4 6-3 to book her place in the third round.
Pole Radwanska, playing in her first premier event as a top seed, said she was pleased with how she had settled in to the event.
"The first match is always the most difficult. Every week we play on different surfaces with different balls and in different conditions. I'm just happy I went through, especially in two sets, because of the heat," she said.
Radwanska will next face Sloane Stephens after the American beat fellow wildcard entrant Camila Giorgi of Italy 6-2 6-1 in an hour.
Her sister Urszula Radwanska, now ranked 46th in the world, progressed to the third round after Kazakh Yaroslava Shvedova retired due to "heat illness".
Denmark's Caroline Wozniacki needed just 59 minutes to dismiss Kazakh Sesil Karatantcheva 6-1 6-0 in a totally one-sided affair.
In the third round Wozniacki will face Russian Anastasia Pavlyuchenkova, who swept aside Germany's Julia Goerges 6-3 6-0.
Results from the third day of the ATP and WTA Cincinnati Masters Series event on Wednesday (x denotes seeding):Women
Agnieszka Radwanska (POL x1) bt Sofia Arvidsson (SWE) 6-4, 6-3
Anastasia Pavlyuchenkova (RUS) bt Julia Goerges (GER) 6-3, 6-0
Sloane Stephens (USA) bt Camille Giorgi (ITA) 6-2, 6-1
Peng Shuai (CHN) bt Roberta Vinci (ITA) 6-3, 6-4
Sara Errani (ITA x7) bt Daniela Hantuchova (SVK) 6-4, 6-4
Andrea Hlavackova, CZE) bt Dominika Cibulkova (SVK x11) 7-6 (7/1), 4-1, retired
Elena Makarova (RUS) bt Anna Tatishvili (GEO) 7-5, 6-2
Petra Kvitova (CZE x4) bt Mona Barthel (GER) 3-6, 6-2, 7-5
Venus Williams (USA) bt Chanelle Scheepers (RSA) 2-6, 6-3, 6-2
Ursula Radwanska (POL) bt Yaroslava Shvedova (KAZ) 4-6, 4-1, retired
Caroline Wozniacki (DEN x6) bt Sesil Karatantcheva (KAZ) 6-1, 6-0
Li Na (CHN x9) bt Sorona Cirstea (ROM) 6-3, 4-6, 6-3
Mardy Fish (USA x10) bt Carlos Berlocq (ARG) 6-3, 6-1
Viktor Troicki (SRB) bt Lleyton Hewitt (AUS) 6-2, 6-0
Nikolay Davydenko (RUS) bt Florian Mayer (GER) 6-3, 6-3
Novak Djokovic (SRB x2) bt Andreas Seppi (ITA) 7-6 (7/4), 6-2
Juan Martin del Potro (ARG x6) bt Tommy Haas (GER) 7-5, 6-2
Andy Murray (GBR x3) bt Sam Querrey (USA) 6-2, 6-4
Radek Stepanek (CZE) bt Juan Monaco (ARG x8) 7-6 (7/2), 6-1
Marin Cilic (CRO x12) bt Jesse Levine (USA) 7-5, 7-6 (8/6)
Jeremy Chardy (FRA) bt Denis Istomin (UZB) 6-4, 6-3
Milos Raonic (CAN) bt Marcos Baghdatis (CYP) 6-7 (6/8), 6-3, 6-4
Roger Federer (SUI x1) bt Alex Bogomolov (RUS) 6-3, 6-2
Pablo Andujar (ESP) bt Janko Tipsarevic (SRB x7) 6-4, 4-1, retired