MELBOURNE, AUSTRALIA - JANUARY 20: Venus Williams and Serena Williams of the United States of America are congratulated by Nadia Petrova of Russia and Katarina Srebotnik Slovenia after winning their third round doubles match during day seven of the 2013 Australian Open at Melbourne Park on January 20, 2013 in Melbourne, Australia. (Photo by Vince Caligiuri/Getty Images)
MELBOURNE, AUSTRALIA - JANUARY 20: Venus Williams and Serena Williams of the United States of America are congratulated by Nadia Petrova of Russia and Katarina Srebotnik Slovenia after winning their third round doubles match during day seven of the 2013 Australian Open at Melbourne Park on January 20, 2013 in Melbourne, Australia. (Photo by Vince Caligiuri/Getty Images)
