Images from Monday's play at the Australian Open
Serena Williams, Novak Djokovic and MIlos Raonic all in action
Serbia's Novak Djokovic reacts after playing a shot during his men's singles match against Luxembourg's Gilles Muller on day eight of the 2015 Australian Open tennis tournament in Melbourne on January 26, 2015.WILLIAM WEST/AFP / Getty Images
Luxembourg's Gilles Muller gestures during his men's singles match against Serbia's Novak Djokovic.WILLIAM WEST/AFP / Getty Images
Gilles Muller of Luxembourg stretches to hit a return to Novak Djokovic of Serbia during their men's singles fourth round match at the Australian Open 2015 tennis tournament in Melbourne January 26, 2015.CARLOS BARRIA/Reuters
Novak Djokovic of Serbia celebrates defeating Gilles Muller of Luxembourg to win their men's singles fourth round match.CARLOS BARRIA/Reuters
David Ferrer of Spain plays a backhand in his fourth round match against Kei Nishikori of Japan.Scott Barbour/Getty Images
Stan Wawrinka of Switzerland looks up before serving against Guillermo Garcia-Lopez of Spain as the court is cleaned during their men's singles match.MAL FAIRCLOUGH/AFP / Getty Images
Poland's Agnieszka Radwanska hits a return against Venus Williams of the US during their women's singles match.MAL FAIRCLOUGH/AFP / Getty Images
Venus Williams plays a shot during her women's singles match against Agnieszka Radwanska.WILLIAM WEST/AFP / Getty Images
Agnieszka Radwanska of Poland stretches out for a shot to Venus Williams of the U.S. during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.Rob Griffith/The Associated Press
Venus Williams shakes hands as she celebrates after victory in her women's singles match against Agnieszka Radwanska.WILLIAM WEST/AFP / Getty Images
Garbine Muguruza of Spain hits a return against Serena Williams of the U.S. in their women's singles match.PAUL CROCK/AFP / Getty Images
Serena Williams hits a return against Garbine Muguruza in their women's singles match on day eight of the 2015 Australian Open tennis tournament in Melbourne.PAUL CROCK/AFP / Getty Images
Serena Williams stretches out for a shot to Garbine Muguruza during their fourth round match.Bernat Armangue/The Associated Press
Serena Williams of the United States reacts to a point in her fourth round match against Garbine Muguruza of Spain.Clive Brunskill/Getty Images
Milos Raonic of Canada stretches for a shot to Feliciano Lopez of Spain.Andy Brownbill/The Associated Press
Spain's Feliciano Lopez plays a shot during his men's singles match against Canada's Milos Raonic.GREG WOOD/AFP / Getty Images
Canada's Milos Raonic plays a shot during his men's singles match against Spain's Feliciano Lopez.MANAN VATSYAYANA/AFP / Getty Images
Milos Raonic signs a Canadian flag after winning his fourth round match against Feliciano Lopez.Michael Dodge/Getty Images
Guillermo Garcia-Lopez of Spain hits a return against Stan Wawrinka of Switzerland in their men's singles match.MAL FAIRCLOUGH/AFP / Getty Images
Guillermo Garcia-Lopez of Spain serves against Stan Wawrinka of Switzerland in their men's singles match.MAL FAIRCLOUGH/AFP / Getty Images
Stan Wawrinka of Switzerland hits a return against Guillermo Garcia-Lopez of Spain.MAL FAIRCLOUGH/AFP / Getty Images
Kei Nishikori of Japan takes off his shirt during his men's singles fourth round match against David Ferrer of Spain.ATHIT PERAWONGMETHA/Reuters
Kei Nishikori of Japan prepares for a serve to David Ferrer of Spain during their fourth round match at the Australian Open.Bernat Armangue/The Associated Press
Kei Nishikori of Japan makes a forehand return to David Ferrer of Spain during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.Rob Griffith/The Associated Press
Madison Brengle of the U.S. hits a return to compatriot Madison Keys during their women's singles fourth round match.THOMAS PETER/Reuters
Madison Brengle of the US plays a shot during her women's singles match against compatriot Madison Keys.GREG WOOD/AFP / Getty Images
Madison Brengle of the United States serves in her fourth round match against Madison Keys of the United States.Cameron Spencer/Getty Images