Breaking: Novak Djokovic has sensationally pulled out of the Australian Open. After dropping the first set to Alexander Zverev in a tie-breaker he turned to the central umpire and withdrew because of his leg injury. He had the top of his left leg heavily strapped. Both players held serve throughout the opening set to force the set into a tie-breaker. Follow the live coverage: https://tinyurl.com/4m7jbtsm