Novak Djokovic pledged to continue his hunt for a record 25th Grand Slam title as he processed the disappointment of retiring from Friday’s Australian Open semi-final due to a muscle injury. Djokovic retired injured after losing the first set 7-6(5) to Alexander Zverev and the 10-times champion made a pained exit from Rod Laver Arena amid booing from sections of the crowd. A look at his Grand Slam titles.