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Novak Djokovic of Serbia watches the ball during his men's singles semi-final match against David Ferrer of Spain at the Australian Open tennis tournament in Melbourne January 24, 2013. REUTERS/Tim Wimborne

Serbia's Novak Djokovic celebrates after defeating Spain's David Ferrer in their semifinal match at the Australian Open tennis championship in Melbourne, Australia, Thursday, Jan. 24, 2013. (AP Photo/Andrew Brownbill)

Spain's David Ferrer hits a return to Serbia's Novak Djokovic during their semifinal match at the Australian Open tennis championship in Melbourne, Australia, Thursday, Jan. 24, 2013. (AP Photo/Aaron Favila)

Sloane Stephens of the U.S. reacts during her women's singles semi-final match against Victoria Azarenka of Belarus at the Australian Open tennis tournament in Melbourne January 24, 2013. REUTERS/David Gray

Novak Djokovic of Serbia hits a return to David Ferrer of Spain during their men's singles semi-final match at the Australian Open tennis tournament in Melbourne, January 24, 2013. REUTERS/David Gray

Novak Djokovic of Serbia (R) speaks with David Ferrer of Spain after defeating him in their men's singles semi-final match at the Australian Open tennis tournament in Melbourne, January 24, 2013. REUTERS/Tim Wimborne

David Ferrer of Spain (R) hits a return to Novak Djokovic of Serbia during their men's singles semi-final match at the Australian Open tennis tournament in Melbourne January 24, 2013. REUTERS/Toby Melville

Victoria Azarenka of Belarus reacts after losing a point in her Semifinal match against Sloane Stephens of the United States during day eleven of the 2013 Australian Open at Melbourne Park on January 24, 2013 in Melbourne, Australia. (Photo by Cameron Spencer/Getty Images)

Sloane Stephens of the United States of America plays a forehand in her Semifinal match against Victoria Azarenka of Belarus during day eleven of the 2013 Australian Open at Melbourne Park on January 24, 2013 in Melbourne, Australia. (Photo by Ryan Pierse/Getty Images)

Victoria Azarenka of Belarus plays a backhand in her Semifinal match against Sloane Stephens of the United States during day eleven of the 2013 Australian Open at Melbourne Park on January 24, 2013 in Melbourne, Australia. (Photo by Ryan Pierse/Getty Images)

Novak Djokovic of Serbia signs autographs for fans after winning his Semifinal match against David Ferrer of Spain during day eleven of the 2013 Australian Open at Melbourne Park on January 24, 2013 in Melbourne, Australia. (Photo by Michael Dodge/Getty Images)

David Ferrer of Spain plays a forehand in his Semifinal match against Novak Djokovic of Serbia during day eleven of the 2013 Australian Open at Melbourne Park on January 24, 2013 in Melbourne, Australia. (Photo by Michael Dodge/Getty Images)

Novak Djokovic of Serbia prepares to receive serve in his Semifinal match against David Ferrer of Spain during day eleven of the 2013 Australian Open at Melbourne Park on January 24, 2013 in Melbourne, Australia. (Photo by Marianna Massey/Getty Images)

Pat Cash of Australia hits a backhand volley during his legends doubles match with Goran Ivanisevic of Croatia against Henry Leconte and Guy Forget of France during the 2013 Australian Open at Melbourne Park on January 24, 2013 in Melbourne, Australia. (Photo by Michael Dodge/Getty Images)

Novak Djockovic walks off after playing the doctor who revived Henry Leconte of France during the legends doubles match with Guy Forget of France against Pat Cash of Australia and Goran Ivanisevic of Croatia during the 2013 Australian Open at Melbourne Park on January 24, 2013 in Melbourne, Australia. (Photo by Michael Dodge/Getty Images)

Sloane Stephens of the US plays a return during her women's singles semi-final match against Belarus's Victoria Azarenka on the eleventh day of the Australian Open tennis tournament in Melbourne on January 24, 2013. GREG WOOD/AFP/Getty Images

China's Li Na (L) shakes hands with Russia's Maria Sharapova after her victory during their women's singles semi-final match on day 11 of the Australian Open tennis tournament in Melbourne on January 24, 2013. PETER PARKS/AFP/Getty Images

Russia's Maria Sharapova serves during her women's singles semi-final match against China's Li Na on the eleventh day of the Australian Open tennis tournament in Melbourne on January 24, 2013. PAUL CROCK/AFP/Getty Images

Russia's Maria Sharapova serves against China's Li Na during their women's singles semi-final match on day 11 of the Australian Open tennis tournament in Melbourne on January 24, 2013. PETER PARKS/AFP/Getty Images

Sloane Stephens of the US hits a return against Belarus's Victoria Azarenka during their women's singles semi-final match on day 11 of the Australian Open tennis tournament in Melbourne on January 24, 2013. WILLIAM WEST/AFP/Getty Images

Spain's David Ferrer plays a return during his men's singles semi-final match against Serbia's Novak Djokovic on the eleventh day of the Australian Open tennis tournament in Melbourne on January 24, 2013. GREG WOOD/AFP/Getty Images

Serbia's Novak Djokovic signs autographs after victory in his men's singles semi-final match against Spain's David Ferrer on the eleventh day of the Australian Open tennis tournament in Melbourne on January 24, 2013. PAUL CROCK/AFP/Getty Images

Serbia's Novak Djokovic (L) shakes hands with Spain's David Ferrer after his victory during their men's singles semi-final match on day 11 of the Australian Open tennis tournament in Melbourne on January 24, 2013. WILLIAM WEST/AFP/Getty Images

Russia's Maria Sharapova plays a return during her women's singles semi-final match against China's Li Na on the eleventh day of the Australian Open tennis tournament in Melbourne on January 24, 2013. PAUL CROCK/AFP/Getty Images

The crowd applauds as Serbia's Novak Djokovic celebrates after defeating Spain's David Ferrer in their semifinal match at the Australian Open tennis championship in Melbourne, Australia, Thursday, Jan. 24, 2013. (AP Photo/Andy Wong)

Victoria Azarenka of Belarus receives treatment from a trainer during her semifinal match against Sloane Stephens of the US at the Australian Open tennis championship in Melbourne, Australia, Thursday, Jan. 24, 2013. (AP Photo/Andrew Brownbill)

Sloane Stephens of the US reacts during her semifinal match against Victoria Azarenka of Belarus at the Australian Open tennis championship in Melbourne, Australia, Thursday, Jan. 24, 2013. (AP Photo/Aaron Favila)

Victoria Azarenka of Belarus signs autographs after defeating Sloane Stephens of the US in their semifinal match at the Australian Open tennis championship in Melbourne, Australia, Thursday, Jan. 24, 2013. (AP Photo/Aaron Favila)

Sloane Stephens, left, of the US congratulates Victoria Azarenka of Belarus after their semifinal match at the Australian Open tennis championship in Melbourne, Australia, Thursday, Jan. 24, 2013. (AP Photo/Aaron Favila)