After losing the first set 6-4, Djokovic was serving to stay in the second set at 5-3 down when he approached the net to try and finish a point.
Musetti attempted a crosscourt passing shot that just went wide and Djokovic was handed the point.
However, Djokovic quickly admitted to the chair umpire that he touched the ball before it went wide and conceded the point to Musetti.
Shortly afterwards, the match ended in unfortunate circumstances as Musetti was forced to retire due to injury while two sets up, handing Djokovic his spot in another Australian Open semi-final.