MELBOURNE: 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. Second seed Rafa Nadal and Greek wunderkind Stefanos Tsitsipas will meet in the other semi-final on Thursday. Djokovic, bidding for a record seventh title in Melbourne, failed to reach the last four in the past two editions of the tournament as he battled with an elbow problem. But he has roared back to his best, and is a huge favourite to win a third successive Grand Slam title after triumphing at Wimbledon and the U.S. Open. “This has been my most successful Grand Slam throughout my career, the first one that I won back in 2008. As I said on the court, I have a lot of beautiful memories from Rod Laver Arena,” he told reporters.