MELBOURNE, Australia -- The world comes to Melbourne Park for the Australian Open and, increasingly, brings its troubles along.
Ethnic passions boiled over for the third year in a row as Serbian and Bosnian supporters clashed on tournament grounds shortly after Serbia's Novak Djokovic completed his 6-2, 4-6, 6-3, 7-6 (4) defeat of Bosnian-born American Amer Delic.
"I'm really sad to hear about that," said Delic, who had posted a Web site message appealing for calm following disruptions in his previous match. "There's absolutely no place for that here. This is a tennis match."
The match itself was played in relatively normal conditions in Rod Laver Arena. Djokovic shied away from the issue afterward, saying it was up to tournament officials to maintain control.
"I can't do much. I'm on the court, I have to keep my focus on the tennis because I need to win the match," Djokovic said. "As I said, authorities are there -- chair umpires, referees, the people, security."
Marian Vajda, Djokovic's coach, said the tensions were disruptive to the players. "Sometimes they are supporting really fully, and sometimes really foolishly," he said. "It's kind of difficult to handle the pressure sometimes. Sometimes, some of them are not well-educated in tennis.
"But the players on the court, they were very nice, very fair and they showed the people how it should be."
The conflicts have usually involved young Australian-born fans of Balkan descent who have carried over local soccer club rivalries into tennis. Eyewitnesses said the scuffle began when Serbian celebrations began to ruffle nearby Bosnian supporters and escalated into what state police described as a "chair-throwing competition."
One woman, an innocent bystander, was hit by a chair but did not suffer serious injury. Two people were charged by police and 30 people, mostly in their late teens or early 20s, were evicted from the site. There was more fighting outside the grounds, but police reported that it was quickly brought under control.
In yet another bizarre incident, a streaker was arrested on Court 3 during a doubles match involving the Williams sisters.
Friday's clash follows a charged atmosphere on the grounds two days ago, when there was a match between Croatia's Marin Cilic and Serbia's Janko Tipsarevic, and another between Delic and bewildered Frenchman Paul-Henri Mathieu.
After Cilic wrapped up a four-set win over Tipsarevic, Serbian fans made their way over to Delic's match, getting involved in a chanting war with the Bosnian fans. Later, conflict between Serbian and Croatian supporters at a bar led to two people being evicted.
Last year, there was controversy after police used pepper spray on boisterous fans during a match between Chile's Fernando Gonzalez and Greece's Konstantinos Economidis. And in 2007, 150 people were evicted after a clash between Serbian and Croatian supporters.
Police can ban offenders from the grounds for 24 hours and issue a fine of AUD $227. But tournament officials have no plans to ban national regalia from the grounds.
Patriotic fans have become a feature of the Australian Open, helping to give the event a festive atmosphere. Groups of face-painted or flag-carrying spectators are a fixture at matches involving Swedes, Dutch, Greeks, Chileans, Serbs, Croats and players from other countries.
Australian coach Bob Brett, who is currently working with Cilic and has been attending the tournament since 1965, said nationalistic displays became common after the event moved in 1988 from a private club at nearby Kooyong to the public facility at Melbourne Park.
"When it came to this stadium, it really made a big difference," Brett said.
He also coached Wimbledon champ Goran Ivanisevic, a Croatian, in the 1990s and says that while the rabid fans were present even then, it is the rise of tennis success among the other Balkan nations that is now creating the conditions for conflict.
"With Goran, when I was working with him, the Croats were coming out in force -- but he never had to play a Serbian," Brett pointed out.
Ivan Ljubicic, also a Croat, said he doesn't like the nature of the support.
"I always felt like they're coming here for political reasons instead of really supporting players," he said. "We always like to have the crowd on our side if they want you to win and they cheer you on. But if they start singing songs that have nothing to do with tennis ... making the point that Croatia is a country now and stuff like that, which doesn't really make sense."
The 29-year-old veteran has never come across this kind of phenomenon anywhere else on the circuit.
"The Croatians here in Australia are different here than anywhere else," he said. "That's the people here, and it's been like that in the past and it's always going to be like this. I don't think it's going to change.
"It doesn't bother me personally, I would just love them to put their energy supporting players instead of making those kind of statements."
The second week of the tournament is likely to bring calm to the grounds, with fewer matches on the outside courts and the bulk of the action taking place in the stadiums, where tickets are more expensive and security is tighter.
But the Serbs, Croats, Bosnians and the rest of tennis' United Nations will be back on these courts next year, and unless the political temperature can be cooled, the potential for trouble will only continue to rise.
Kamakshi Tandon is a freelance tennis writer for ESPN.com.