Serbia's Novak Djokovic and Serena Williams of the US perform the gangnam style dance during the Kids Tennis Day at Melbourne Park ahead of the Australian Open tennis championship in Melbourne, Australia, Saturday, Jan. 12, 2013. (AP Photo/Andy Wong)
Serbia's Novak Djokovic and Serena Williams of the US perform the gangnam style dance during the Kids Tennis Day at Melbourne Park ahead of the Australian Open tennis championship in Melbourne, Australia, Saturday, Jan. 12, 2013. (AP Photo/Andy Wong)
Serbia's player Novak Djokovic reacts during his match against Sam Querrey of the U.S. at the Paris Tennis Masters tournament, Wednesday, Oct. 31, 2012. Sam Querrey defeated Novak Djokovic. (AP Photo/Remy de la Mauviniere)
Serbia's player Novak Djokovic reacts during his match against Sam Querrey of the U.S. at the Paris Tennis Masters tournament, Wednesday, Oct. 31, 2012. Sam Querrey defeated Novak Djokovic. (AP Photo/Remy de la Mauviniere)
associated press photographs 12th-seeded Jo-Wilfried Tsonga celebrates after defeating Roger Federer. Tsonga will Novak Djokovic, who is 46-1 this season, in the semifinals Friday.
