Serena and Venus Williams won their second-round singles matches at the U.S. Open, setting up yet another sisterly showdown in the third round on Friday, August 31. For Serena, 36, and Venus, 38, this will be the 30th match they've played against each other in their careers, a rivalry that has always sat a little uneasily with them both. "I never root against her, no matter what. So I think that's the toughest part for me," said Serena after her second-round win. Whether they're facing each other or playing in doubles tournaments, Serena and Venus together always amp the excitement of any competition they're in. Here, a brief look back at the Williams sisters on the court.Quinn Rooney/Getty Images AUSSIE VICTORY Kevork Djansezian/Getty Images PRE-GAME
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