Novak Djokovic through to Australian Open semi-finals after Kei Nishikori retires

Novak Djokovic is through to the semi-finals of the Australian Open after Kei Nishikori retired from their quarter-final clash in the second set.

Nishikori came into the match against the no.1 seed having spent been on court for more than three hours longer than his opponent, and it showed.

After being broken in his first service game, Nishikori looked uncomfortably throughout and called his trainer having lost the opening set 6-1.

Two more breaks of serve spelt the end of the no.8 seed in front of the large Japanese following inside the Rod Laver Arena as he retired at 4-1 in the second set.

"I hope he can recover," Djokovic said after the match. "I hope it’s not something very serious. I wish him a speedy recovery. I’m sorry to everybody for not having a full match but thank you for showing up."

He added: "I am in another semi-finals and I will do everything to get ready for that one."

Djokovic will face Lucas Pouille in the semi-finals, with no.2 seed Rafael Nadal battling against young star Stefanos Tsitsipas.