Djokovic got off to a sharp start against Musetti, broke quickly, but then spectacularly lost his way.

A horrifying overhead mistake forced Musetti to break him back, but Djokovic never recovered, dropping just one ace and making 18 unforced errors against nine winners and nearly losing the first set.

Djokovic frequently turned his head toward the box in disbelief and frustration, but was only held accountable at the start of the second set.

After defeating Musetti and opening up a 30-0 lead on serve, Djokovic made five unforced errors in six points to regain control.

Armed with Djokovic’s predictable one-handed backhand and improved serve, Musetti kept his opponent at bay and came within striking distance of the first Australian Open semi-final match.

The injury was even more surprising considering Musetti’s level. After being broken in the third set, he immediately called for his trainer and after a valiant attempt at his next service game, called off the match.

Djokovic had kind words for his opponent online and after the match – no doubt aware of how devastated the 23-year-old, who has struggled with physical problems early in his career, was feeling.

Despite his good fortune, Djokovic will know he needs to improve if he is to win an 11th Australian Open title, with two-time defending champion Jannik Sinner potentially waiting in the top four.

World No. 2 Sinner, who defeated Djokovic in the semifinals two years ago, will face eighth-seeded American Ben Shelton later on Wednesday.