Djokovic -- who's been on edge in the major tournament Down Under as he's fighting through an abdominal injury -- was in a heated quarter-final match with Alexander Zverev when he lost his cool.

Tennis' #1-ranked player returned a key serve in the third set into the net ... and then melted down.

He let out a massive yell, slammed his racket into the court three times ... and then walked to his bench and threw the destroyed piece of equipment down angrily.

The temper tantrum left such a mess on the court, a ball person actually had to sweep up all the debris. The court itself, meanwhile, had three scars in it!!

Djokovic, though, was NOT penalized for the outburst ... and he ended up battling his way to a victory. Afterward, Novak admitted he felt "drained."

Of course, the 33-year-old is no stranger to outbursts on the court ... remember, he was disqualified from the U.S. Open back in September after he angrily and haphazardly hit a ball at a lineswoman.