The 37-year-old Serb, who is chasing a record 25th Grand Slam crown, outlasted the Spaniard, 16 years his junior, 4-6, 6-4, 6-3, 6-4 despite having his left thigh heavily strapped.

It was a vintage 3hrs 37mins performance and put him into the last four at Melbourne Park for a 12th time, with only Roger Federer (15) doing so more often.

The win also extended his all-time record for most Grand Slam semi-final appearances to 50, four clear of the Swiss great.

To reach another final, he will need to beat second seed Zverev, who battled into the last four for a second year running with a 7-6 (7/1), 7-6 (7/0), 2-6, 6-1 win over American 12th seed Tommy Paul.

As the wind swirled, Djokovic opened with a commanding hold then broke immediately as Alcaraz struggled to find his range.

But the advantage was short-lived with the world number three Spaniard rifling a backhand down the line to break straight back.

Seventh seed Djokovic saved two break points in an enthralling game nine, but appeared to be wincing and Alcaraz converted on the third for a 5-4 lead when the veteran sprayed a forehand wide.

The Serb called the trainer and left court for a medical timeout after the game, with Alcaraz sealing the set to love on his return.

But Djokovic, with his thigh strapped, wasn't done and broke to race 3-0 ahead in set two, playing more aggressively.

Alcaraz then won three games in a row to seemingly seize control, but Djokovic pulled off a break to love from nowhere with a backhand winner to take the set.

An intense third set went with serve until three breaks in a row left Djokovic 5-3 ahead and able to serve out, blowing kisses to his children in the crowd as the stadium erupted.

Djokovic had all the momentum and broke straight away in the fourth set. Both men produced some sensational tennis, including a 33-shot rally, before Alcaraz finally succumbed.

- The greatest -

Zverev came good when it mattered as he edged closer to his dream of a maiden Grand Slam title.

The German also reached the semis in 2020, losing to Dominic Thiem, and again last year when he crashed to Daniil Medvedev in five sets despite holding a 2-0 lead.

He has played Djokovic 12 times before dating back to 2017, with the Serb holding an 8-4 record, including victory when they last met in 2023 at Cincinnati.

"Two of the best players that have ever touched a tennis racquet," said Zverev of Djokovic and Alcaraz.

"Novak is the greatest of all time right now. Carlos is going to be one of them when he hangs it up so it is a clash of generations."

Bidding to become the first German man to win a Grand Slam since Boris Becker in 1996, Zverev was made to work hard by Paul.

But he asserted himself when it mattered in the tiebreaks and won the fourth set emphatically.

"I'm going to prepare myself for a very intense and high-level match," he said on the semi-final.