While age is clearly catching up on Djokovic, his insatiable appetite for Grand Slam success shows no signs of slowing down.

A patchy season by his lofty standards has led to questions about his stamina and motivation, while the departure of rival-turned-coach Andy Murray from his team also indicated things were not functioning as he hoped.

But when the major tournaments come around, Djokovic is always still primed to challenge in the latter stages.

In Melbourne, he defied the odds to beat Alcaraz and reach the semi-finals, although the physical exertions led to a hamstring tear which meant he had to retire injured against Zverev in the last-four encounter.

Nevertheless, it showed he still had the desire and capability to beat the younger generation over the five-set format.

“I think the win against Alcaraz and against Zverev tonight proves to myself and others that I can still play at the highest level,” Djokovic said.

“I just thrive on these occasions. This is where I lock in and really give my best.”

Zverev, 28, was once part of the first crop expected to replace Djokovic, Murray, Rafael Nadal and Roger Federer.

This defeat was another illustration of how the German is often unable to problem-solve against Djokovic, who won four of his eight break points.

Often accused of being too passive, Zverev was rooted deep behind the baseline for much of the contest and paid the price as Djokovic took control with his craftmanship.

With belief or focus rarely wavering, the Serb started dictating the patterns of play and used the drop shot effectively to unsettle Zverev.

When the three-time Grand Slam runner-up finally thought his chance of a comeback had arrived midway through the fourth set, he was denied in arguably the point of the tournament.

Djokovic showed all his elasticity and endurance to stop Zverev putting the set back on serve.

It enabled Djokovic to serve out victory after three hours and 17 minutes as another deft drop shot, fittingly, caught out Zverev again.