Djokovic went through a dramatic match and, after losing the third set, fought back, beating his Austrian opponent in five sets -- 6-4, 4-6, 2-6, 6-3, 6-4.
Djokovic, who remains unbeaten in finals on Rod Laver Arena, now has 17 slam titles, only three short of record holder Roger Federer, and will reclaim the world No 1 ranking from Nadal on Monday.
Austria's Dominic Thiem beat Germany's Alexander Zverev 3-1 on Jan. 31 to earn his spot in the 2020 Australian Open men's final.
Fifth-seeded Thim won against seventh-seeded Zverev with 3-6, 6-4, 7-6, 7-6 sets in semifinals at Melbourne's Rod Laver Arena.
On Jan. 30, Novak Djokovic eliminated Roger Federer 3-0 to earn his spot in the 2020 Australian Open men's final.
It took Serbian player almost three hours of play to reach his eighth semifinal in Melbourne.
An old acquaintance and a big rival Roger Federer, who eliminated Tennys Sandgren in quite a dramatic match, awaits him in the semi-final blockbuster.
Interestingly, whenever he reached semi-finals of the tournament in Melbourne, Djokovic would win it.
Sixth seed Stefanos Tsitsipas has advanced to the third round of the Australian Open after his German opponent Philipp Kohlschreiber withdrew due to injury, organizers said on Wednesday.
ATP Finals champion Tsitsipas, 21, will meet either Canadian 32nd seed Milos Raonic or Cristian Garin of Chile in the third round, having never faced either opponent before.