Wednesday 23 January 2019 12:38, UK
Novak Djokovic progressed into the Australian Open semi-finals when Kei Nishikori retired due to injury.
Djokovic was leading 6-1 4-1 in the quarter-final when Nishikori decided he was unable to continue due to a thigh problem.
Top seed Djokovic will now play Lucas Pouille, who beat Milos Raonic 7-6 (7-4) 6-3 6-7 (2-7) 6-4, for a place in the final.
"I love to battle, especially against Kei, we've played so many matches," said Djokovic.
"I hope he can recover, I hope it's not something that is very serious. I'm sorry for everybody for not having a full match tonight."
Djokovic had endured his own physical battle against Daniil Medvedev on Monday and admitted afterwards that he was feeling the effects.
"This is exactly what the doctor ordered," he said, "Not to spend too much time on the court. I'm in another semi-final and I'll do everything to get ready for that one."
Rafael Nadal meets Stefanos Tsitsipas, who eliminated Roger Federer, in the other semi-final.
Djokovic is looking to claim his seventh title in Melbourne, having won the Grand Slam on every previous occasion that he has made the final four.
His route out of the last eight was ultimately straightforward due to Nishikori's fitness issues.
The Japanese eighth seed required a medical time-out between sets because of problems with his right thigh.
By the premature end to the match, Nishikori was visibly exhausted and hardly able to move.
He had played three five-set matches at the tournament before the quarter-final.
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