As good as Djokovic is, we have to remember that he's only human. No matter how superhuman his efforts might look, he is not perfect, and he is capable of losing a tennis match, especially under the circumstances he faced this year in Melbourne.
He hasn't lost many of them in recent years, and certainly not in Melbourne, but Jannik Sinner has been the best-performing player in recent months, so he didn't just lose to some random player.
According to Ivanisevic, he was bound to lose someday anyway. Talking to Sportske Novosti during Croatia's Davis Cup tie, Ivanisevic looked back on the Australian Open, sharing some of his thoughts on how things unfolded. It didn't go the way Djokovic or his team planned, but that's life.
"Sooner or later he had to lose, we were all aware of that. It's just a shame that it happened this way, but against Sinner if you're not 100%, you have nothing to ask for. And even when you're at 100%, you can still lose."
Depending on how you read that, you might assume that Ivanisevic hints at Djokovic not being 100%, but he denied that in the same interview. Still, it seemed that, indeed, the Serbian was struggling with some type of injury since the whole injury drama that happened at the United Cup and in the matches since then.
Djokovic won Grand Slams while injured, last year being a case in point, but Sinner was too strong on that day. It wasn't a particularly close match, and the writing was on the wall. As Ivanisevic pointed out, the event never looked right for Djokovic from start to finish.
"However, the whole Australian Open was somehow not right for Novak, from the first round onwards. Well, let's move on, it's nothing so tragic."