Serena Williams

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FILE - In this Jan. 11, 2014 photo, Serena Williams of the United States speaks during a news conference ahead of the Australian Open tennis championship in Melbourne, Australia. Beats by Dre, the headphone company held two events Friday, Jan. 31, 2014. Williams along with other celebrities Anthony Mackie, Jerry Stackhouse, and Jermaine Dupri attended a performance by British singer Estelle. (AP Photo/Aaron Favila)

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Ana Ivanovic of Serbia celebrates her win over Serena Williams of the U.S. in their fourth round match at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 19, 2014.(AP Photo/Andrew Brownbill)

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Ana Ivanovic of Serbia celebrates her win over Serena Williams of the U.S. during their fourth round match at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 19, 2014.(AP Photo/Aaron Favila)

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Ana Ivanovic of Serbia, left, is congratulated by Serena Williams of the U.S. after Ivanovic's fourth round win at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 19, 2014.(AP Photo/Aaron Favila)

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Serena Williams of the U.S. rests on her racket during her fourth round loss to Ana Ivanovic of Serbia at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 19, 2014.(AP Photo/Aaron Favila)

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Serena Williams of the U.S. speaks during a press conference after her fourth round loss to Ana Ivanovic of Serbia at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 19, 2014. (AP Photo/Shuji Kajiyama)

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Ana Ivanovic of Serbia waves to the crowd as she celebrates her win over Serena Williams of the U.S. in their fourth round match at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 19, 2014.(AP Photo/Aaron Favila)

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Ana Ivanovic of Serbia celebrates a point won against Serena Williams of the U.S. during their fourth round match at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 19, 2014. (AP Photo/Aaron Favila)

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Serena Williams of the U.S. supports herself with a racket as she plays Ana Ivanovic of Serbia during their fourth round match at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 19, 2014.(AP Photo/Aaron Favila)

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Serena Williams of the U.S. celebrates after defeating Daniela Hantuchova of Slovakia in their third round match at the Australian Open tennis championship in Melbourne, Australia, Friday, Jan. 17, 2014.(AP Photo/Aaron Favila)

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Serena Williams of the U.S. makes a backhand return to Daniela Hantuchova of Slovakia during their third round match at the Australian Open tennis championship in Melbourne, Australia, Friday, Jan. 17, 2014.(AP Photo/Aaron Favila)

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Serena Williams of the U.S. cools down with ice towel on her shoulders between games during her third round match against Daniela Hantuchova of Slovakia at the Australian Open tennis championship in Melbourne, Australia, Friday, Jan. 17, 2014. (AP Photo/Aaron Favila)