PHOTOS: Djokovic through to semis after Nishikori retires

Novak Djokovic reached the semi-finals of the Australian Open for a seventh time on Wednesday after eighth seed Kei Nishikori retired hurt when trailing 6-1 4-1 in their quarter-final.

Top seed and six-times champion Djokovic will meet Frenchman Lucas Pouille, a maiden Grand Slam semi-finalist, on Friday for a place in Sunday's final.

Rafael Nadal and Greek wunderkind Stefanos Tsitsipas will meet in the other semi-final on Thursday.

Nishikori, who grinded through three five-set matches at the tournament, was clearly struggling after a handful of games in the evening match at Rod Laver Arena and had a medical time-out after losing the first set.

He grimaced as a trainer worked on his right thigh and pulled out of the match after Djokovic won the fifth game.

Although appearing untroubled by any injury niggles, Djokovic was grateful for the short match, having complained of a sore back and a "couple of issues" after battling through a taxing four-set clash against Russian Daniil Medvedev in the previous round.

"As they say this is exactly what the doctor ordered," he told Jim Courier in their on-court interview.

"I've had plenty of matches so far this year .. And I'll do everything to get ready for that (next) one."

Pouille edges Raonic to reach maiden Grand Slam semis

Frenchman Lucas Pouille tamed big-serving Milos Raonic 7-6(4), 6-3, 6-7(2), 6-4 in the Australian Open quarter-final to advance to his maiden Grand Slam semi-final.

The Frenchman, 24, took the first set with a brilliant forehand pass against an advancing Raonic in the tiebreak and converted his only breakpoint opportunity in the second set with a measured backhand lob before two winners and two big serves gave Pouille the second stanza.

The 28-year-old Raonic made former top 10 player Pouille pay for wasting four breakpoints by winning the third set tiebreaker but the Frenchman broke the Canadian again in the fourth, converting his third matchpoint to seal the contest in just over three hours.

Pouille will meet the winner of the last quarter-final between top-seeded Serb Novak Djokovic and Kei Nishikori of Japan for a place in Sunday's final.