Two-time champion Venus Williams pulled out of the U.S. Open on Wednesday, citing an autoimmune disorder, while former champion Maria Sharapova advanced to the third round.
Last year's runner-up Vera Zvonareva was an easy opening-day winner, while Wimbledon champion Petra Kvitova came up a first-round upset victim Monday at the 2011 U.S. Open.
Former champions Caroline Wozniacki and Sam Stosur were a pair of easy second-round winners Wednesday at the Family Circle Cup tennis event, while Venus Williams advanced despite receiving a tougher test in her match.
The women's doubles juggernaut of Serena Williams and Venus Williams posted a quarterfinal victory Thursday by topping the top seeds at the 2013 U.S. Open.
Reigning champion Serena Williams was an easy second-round winner, while Sara Errani became the highest-seeded loser to this point at the 2013 U.S. Open.