Djokovic, who is chasing a record-extending 11th Melbourne title and historic 25th Grand Slam crown, is on a collision course with Alcaraz in the quarter-finals.

Both kept that tantalising prospect alive with ruthless victories.

Under new coach and old rival Andy Murray, the 37-year-old Djokovic needed four sets in both of his opening two matches.

But not this time, swatting aside Czech 26th seed Tomas Machac 6-1, 6-4, 6-4 and letting out a roar at the end.

Djokovic also pointed to his ear and then someone in the Rod Laver Arena crowd.

"I am very hot-headed right now," said the fiery Serb, but added: "This is definitely the best match I played at this tournament."

Djokovic, who needed a medical break in the second set and used an inhaler, faces 24th seed Jiri Lehecka next.