Novak Djokovic dramatically retired from his Australian Open semi-final against Alexander Zverev after being unable to play through a torn muscle in his upper left leg before admitting there is a “chance” may have played at the tournament for the final time.

Ben Shelton has reached his first Australian Open semifinal by defeating Lorenzo Sonego 6-4, 7-5, 4-6, 7-6 in an entertaining match.