Australian Open Day 12: Stefanos Tsitsipas and Novak Djokovic in final

Tennis superstar Novak Djokovic was left seeing red on Friday night with the umpire copping the Serbian's wrath.

The singles finals are locked in after an epic day of action again at Melbourne Park.

On Thursday, Elena Rybakina and Aryna Sabalenka booked their spot in the women's singles final with straight set wins over Victoria Azarenka and Magda Linette, respectively. 

Stefanos Tsitsipas took care of business in four sets against Karen Khachanov to book a spot in his first ever Australian Open men's final.

He'll take on nine-time Australian Open winner Novak Djokovic  who comfortably took care of business against unseeded American Tommy Paul.

The winner of the final will take over as the number one ranked player in the world which would be the first time ever for Tsitsipas. The Greek star can also become the first player in the history of tennis to win a Grand Slam for Greece.

For Novak a win on Sunday would see him equal Rafael Nadal on the all-time Grand Slam winners list with 22.

But while Djokovic dominated after a tight first set, the stress of a first set tiebreaker was getting to the Serbian superstar.

After racing away to a 5-1 lead in the opening set, Paul produced a fightback for the ages as he turned the tables on Djokovic and snatched four games on the trot.

In the midst of it all, the Serbian had a mini-meltdown as he lost his cool among the shifting tides.

Novak was getting frustrated in the first. Photo by Clive Brunskill/Getty Images

The Serbian lost his cool during the seventh game of the opening set when he walked over to grab his towel only to realise the serve clock had started. He immediately made a bee-line for the chair umpire and had some stern words with him.

"The ball kids are not allowed to give me the towel. Tell me how it works if it's not working," Djokovic fumed at the umpire.

"It's the first time I'm getting the towel in this game."

Channel Nine commentator Jim Courier clarified the rules surrounding the serve clock that had left Djokovic seeing red.

"The way it works is it starts when the chair umpire calls the score. It's not when a player gets to the towel box. That is a misunderstanding of the rule from Novak. If it's a quick point, like an ace, the clock will start a lot faster than if it is a 10-shot rally," Courier said on the coverage.

The women's final featuring Rybakina and Azarenka will take place on Saturday night, followed by the men's doubles final with Aussie duo Jason Kubler and Rinky Hijikata playing Monaco's  Hugo Nys and Poland's Jan Zielinski.

The women's doubles featuring top seeds Barbora Krejcikova and Katerina Siniakova Vs Japanese 10th seeds Shuko Aoyama and Ena Shibahara will be played on Sunday morning before the men's singles final between Djokovic and Tsitsipas.

However, it was a momentary lapse for Djokovic, who bounced back and showed his ruthlessness in another lopsided semi-final.

Three of the four semi-finals were straight sets finishes, while Tsitsipas lost the third set of his match against Karen Khachanov despite having ample opportunity with three match points before the Russian pushed it to four.