Serena Williams of the United States serves during her women's singles second-round match against Galina Voskoboeva of Kazakhstan on Day 4 of the 2013 US Open at USTA Billie Jean King National Tennis Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
Roger Federer of Switzerland plays against Carlos Berlocq of Argentina during their 2013 US Open singles match at the USTA Billie Jean King National Tennis Center in Flushing on Aug. 29, 2013. (credit: Getty Images)
US Open Day 4
Ana Ivanovic of Serbia serves to Alexandra Dulgheru of Romania during their 2013 US Open women's singles match at the USTA Billie Jean King National Tennis Center Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
Sabine Lisicki of Germany returns the ball to Paula Ormaechea during their US Open 2013 women's singles match at the USTA Billie Jean King National Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
Roger Federer of Switzerland returns a shot during his men's singles second-round match against Carlos Berlocq of Argentina on Day 4 of the 2013 US Open at USTA Billie Jean King National Tennis Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
Bernard Tomic of Australia serves during his men's singles second-round match against Daniel Evans of Great Britain on Day 4 of the 2013 US Open at USTA Billie Jean King National Tennis Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
Aleksandra Wozniak of Canada returns a shot to Victoria Azarenka of Belarus during their 2013 US Open women's singles match at the USTA Billie Jean King National Tennis Center Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
Children with oversized tennis balls wait for Victoria Azarenka of Belarus to sign autographs after she defeated Aleksandra Wozniak of Canada during their 2013 US Open women's singles match at the USTA Billie Jean King National Tennis Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
David Ferrer of Spain plays a forehand during his men's singles second-round match against Roberto Bautista Agut of Spain on Day 4 of the 2013 US Open at USTA Billie Jean King National Tennis Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)
2013 US Open - Day 4
Ashleigh Barty of Australia serves next to her partner, Casey Dellacqua of Australia, during their women's doubles first-round match against Sorana Cirstea of Romania and Yanina Wickmayer of Belgium on Day 4 of the 2013 US Open at USTA Billie Jean King National Tennis Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
Victoria Azarenka of Belarus signs autographs following her victory in her women's singles second-round match against Aleksandra Wozniak of Canada on Day 4 of the 2013 US Open at the USTA Billie Jean King National Tennis Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
A general view of Louis Armstrong Stadium during the women's singles second-round match between Victoria Azarenka of Belarus and Aleksandra Wozniak of Canada on Day 4 of the 2013 US Open at the USTA Billie Jean King National Tennis Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
Victoria Azarenka of Belarus reacts during her women's singles second-round match against Aleksandra Wozniak of Canada on Day 4 of the 2013 US Open at the USTA Billie Jean King National Tennis Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)
US Open Day 4
Adrian Mannarino of France celebrates his win over Sam Querrey of the United States during their 2013 US Open men's singles match at the USTA Billie Jean King National Tennis Center on Aug. 29, 2013 in Flushing. (credit: Getty Images)