Croatian and Serbian spectators kicked each other and used flag poles as weapons during brief scuffles Monday at the Australian Open.
Police and private security guards at the year's first Grand Slam event ejected 150 people from the Melbourne Park venue after the violence, which organizers, players and community leaders condemned.
Police said no injuries were reported and no arrests were made.
Two groups of mostly male youths dressed in the colors of the former rivals in a bitter early-1990s war chanted slogans and yelled insults at each other near a lawn area where a giant television screen is set up for spectators.
News photographs and footage recorded on mobile phones of the incident showed youths kicking each other and using large hand-held flags as batons. Australian television showed police, some of them with batons drawn, marching supporters out of the venue and escorting them out of the area on trains.
"While we are happy for fans to come along and support their favorite player, decisive action will be taken if any patrons or groups cross the line of acceptable behavior at this family event," Tennis Australia chief Steve Wood said in a statement.
Serbian and Croatian community groups blamed each other for the trouble.
Tom Starcevic, secretary of the Croatian Community Association in Victoria state, said witnesses told him that Serbs provoked the dispute by chanting "Die, Croat, die."
Toma Banjanin, president of the Serbian Cultural Club, blamed Croatian supporters for provoking the incident, accusing them of "mixing politics with sport."
Serbia and Croatia were involved in a brutal war in the early 1990s as the former Yugoslavia crumbled. In Australia, the Croatian and Serbian communities both number in the hundreds of thousands.
Serbian player Jelena Jankovic, a U.S. Open semifinalist last year, said ethnic divisions had no place at the tournament, but that such incidents occurred more in Melbourne -- one of Australia most mixed-ethnic cities -- than elsewhere on the tennis circuit.
"I think just here in Melbourne that there is this kind of problems," she said. "Anywhere else in the world it's fine.
"I don't like when they are fighting against each other and kind of booing the other player just because they are from some other country," she said. "I think that's not fair."
Croatia's Mario Ancic, seeded ninth in the men's draw, said he wasn't aware of Monday's disturbance.
Authorities tightened security at the venue, with Croatian Marin Cilic due to play against Serbia's Ilia Bozoljac in a first-round men's match Tuesday.