Serbia's Novak Djokovic reacts during his fourth round match against Switzerland's Stanislas Wawrinka at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 20, 2013. (AP Photo/Andy Wong)
Serbia's Novak Djokovic reacts during his fourth round match against Switzerland's Stanislas Wawrinka at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 20, 2013. (AP Photo/Andy Wong)