Police at the Australian Open in Melbourne ejected around 150 spectators after a brawl broke out between Serbian and Croatian fans on Monday.
Rival fans scuffle at Melbourne Park
Fans wearing the national colours of the two nations clashed around the Rod Laver Arena.
Dozens of police were forced to separate the two groups before ejecting them and confiscating their tickets.
"They were mostly Serbians ejected as they were upsetting the Croatians," a Victoria state police spokeswoman said.
Tennis Australia chief executive Steve Wood said there were no injuries or arrests and security staff had acted swiftly to end the fight.
It's just a sport and people should just come and enjoy the game
"We hope that today's well co-ordinated response sends a clear message that while we are happy for fans to come along and support their favourite player, decisive action will be taken if any patrons, or groups, cross the line of acceptable behaviour at this family event," he said.
There is likely to be a heavy security presence at Tuesday's match between Serbian Ilia Bozolojac and Croatian Marin Cilic, a potential flashpoint between the rival fans.
The Serbian fans had gathered to support Jelena Jankovic, while the Croats were at the tournament for matches involving Mario Ancic, Karolina Sprem and Ivan Ljubicic.
Jankovic called for calm among the fans, saying "it's just a sport and people should just come and enjoy the game".