A fight broke out in Melbourne Arena ahead of Nick Kyrgios' third round match against Karen Khachanov.
Video footage emerged of a brawl in the lower stands of Melbourne Arena just before 7pm (AEST) on Saturday, minutes before Kyrgios entered the venue.
A woman was allegedly punched by a man and started bleeding, according to a witness claim on Twitter.
One fan was escorted from the venue as a result of the altercation, according to multiple witness claims on social media
Contradicting reports on social media claimed two men were escorted from the venue.
Tennis Australia is investigating the incident.
The Herald Sun reports the incident included a "punch on" — according to one witness.
"It was a bit of a punch-on,'' witness Alex Nikolaou told the newspaper.
"I don't know what started it. All I heard was screaming across the court.
"There were all these people trying to separate the two."
There were wild scenes inside the venue affectionately known as "The People's Court" when Kyrgios walked out onto court for his third round match.
Melbourne Arena is the biggest venue that at the Open that can be accessed by spectators with a groundpass.
The venue was at capacity and was rocking even before the start of the match.
"This crowd is electrified. That was like a rock star on stage when Nick came on," Channel 9's Jim Courier said.
"And when Karen came on, the crowd went mild. This will be a high energy building and if Nick can get off to a good start, it's a good thing they have the roof open tonight."
Aussie tennis great Todd Woodbridge told Channel 9: "The energy is off the charts in this building.
"It's what tennis needs... a high energy crowd, standing room only for the people trying to get in from outside the stadium.
"Obviously we are going to move to Rod Laver Arena and Margaret Court Arena later but this is a nice send-off for Nick Kyrgios in this match in the tournament.