Novak Djokovic held a commanding 6-1, 4-1 lead when Nishikori called it quits.
MELBOURNE — Novak Djokovic advanced to the Australian Open semifinals when Kei Nishikori retired in the second set after less than an hour of play.
Djokovic was leading 6-1, 4-1 when the eighth-seeded Nishikori let the umpire know he couldn't continue. Nishikori, the 2014 U.S. Open runner-up, played three matches that went to five sets in his first four rounds. Two of those went to the new fifth-set super tiebreaker introduced at the Australian Open this year.
Nishikori needed a medical timeout for treatment on his upper leg after the first set. He wasn't comfortable throughout the match, and had his service broken four times.
Djokovic is aiming for a men's record seventh Australian title. He will next play Lucas Pouille, who beat Milos Raonic earlier Wednesday.