Novak Djokovic has not been a happy camper on Rod Laver Arena against Taylor Fritz, taking out his frustration on his own box as well as the umpire at one stage.
The world No 1 is the strong favourite to win an 11th Australian Open crown, but he was always going to face a difficult test against No 12 seed Fritz.
The players were also contesting in blistering heat out on court with frozen towels on hand to try and keep them both cool.
Djokovic appeared to be struggling the most with the heat and he cut an agitated figure at a change of ends with the score 5-6 in the first set.
Novak Djokovic lost his cool with his own team
EUROSPORT
While looking for something in his bag - seemingly something to eat - Djokovic grew frustrated as what he was searching for didn't appear to be there.
He tried to grab the attention of his own team, who weren't paying attention as the Serbian began waving frantically.
Djokovic began screaming loudly at them and before gesturing with his hands for them to start paying attention.
Goran Ivanisevic and the rest of Djokovic's coaching team were then seen looking sheepish in the box before play got back underway.
The exchange nearly proved costly immediately after as Fritz nearly stole the first set away from Djokovic with two set points, but the Serbian saved both before taking the lead in the tiebreak.
The 24-time Grand Slam champion continued to struggle with the conditions though and had breathing problems.
It wasn't only the heat that was getting to Djokovic though as he questioned the umpire why the lights were on despite it still being daylight outside.
"Is it necessary to have the lights so strong while it's still day?" he could be heard asking the umpire.
Novak Djokovic's team looked sheepish after being told off
EUROSPORT
"I mean, they're so strong. Is it really necessary?
"We're seeing just fine."
That agitation only grew stronger after Fritz took the second set to level up the match with players in for a long evening.
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Novak Djokovic was struggling with the heat on court
GETTY
Tennis Australia extended the tournament to 15 days, starting on the Sunday instead of the traditional Monday, this year in an attempt to stop matches going long into the early hours of the morning.
But Djokovic's match against Fritz was part of the day session and was still being played at 8pm local time with two more matches scheduled to be played on Rod Laver Arena later today.
Barbora Krejcikova faces Aryna Sabalenka before Jannik Sinner takes on Andrey Rublev in a hotly-anticipated quarter-final contest.