36-year-old Djokovic took the first set 6-3 before world number one Alcaraz, 20, responded and won the second 7-5.
At the beginning of the third set, the conditions changed considerably.
Alcaraz grimaced and grabbed his right calf, above the knee. Djokovic then went forward to settle the situation with the Spaniard before the match was briefly interrupted and then resumed.
World number one Carlos Alcaraz grimaces badly in the semi-finals against world number three Novak Djokovic.
Alcaraz continued to play the third set, clearly troubled by something, a set that the Serb easily took home with the numbers 6–1.
The big question before the fourth set was whether the Spaniard would be able to complete the match or not.
He could.
Alcaraz started the fourth set energetically, but Djokovic took the first game and then it rolled on.
The Serb finally won the fourth set 6–1 and the match 3–1 in sets.
Either the Norwegian Casper Ruud or the German Alexander Zverev await in the final. If Djokovic wins it, he will have 23 grand slam titles, more than anyone else.