Rafael Nadal of Spain hits a backhand in his quarter final match against Tomas Berdych of the Czech Republic during day nine of the 2012 Australian Open at Melbourne Park on January 24, 2012 in Melbourne, Australia.

Roger Federer

Roger Federer of Switzerland plays a forehand in his quarter final match against Juan Martin Del Potro of Argentina during day nine of the 2012 Australian Open at Melbourne Park on January 24, 2012 in Melbourne, Australia.

Kim Clijsters

Kim Clijsters of Belgium celebrates winning her quarter final match against Caroline Wozniacki of Denmark during day nine of the 2012 Australian Open at Melbourne Park on January 24, 2012 in Melbourne, Australia.

Rafael Nadal

Rafael Nadal of Spain plays a backhand in his quarter final match against Tomas Berdych of the Czech Republic during day nine of the 2012 Australian Open at Melbourne Park on January 24, 2012 in Melbourne, Australia.

Tomas Berdych

Tomas Berdych of the Czech Republic plays a forehand in his quarter final match against Rafael Nadal of Spain during day nine of the 2012 Australian Open at Melbourne Park on January 24, 2012 in Melbourne, Australia.

Rafael Nadal Oz Open

Rafael Nadal of Spain speaks to the umpire after a controversial call in his quarter final match against Tomas Berdych of the Czech Republic during day nine of the 2012 Australian Open at Melbourne Park on January 24, 2012 in Melbourne, Australia.

Victoria Azarenka

Victoria Azarenka of Belarus plays a forehand in her quarter final match against Agnieszka Radwanska of Poland during day nine of the 2012 Australian Open at Melbourne Park on January 24, 2012 in Melbourne, Australia.

Caroline Wozniacki

Caroline Wozniacki of Denmark plays a backhand in her quarter final match against Kim Clijsters of Belgium during day nine of the 2012 Australian Open at Melbourne Park on January 24, 2012 in Melbourne, Australia.

Juan Martin Del Potro

Juan Martin Del Potro of Argentina serves in his quarter final match against Roger Federer of Switzerland during day nine of the 2012 Australian Open at Melbourne Park on January 24, 2012 in Melbourne, Australia.