MELBOURNE, Australia — Boisterous Bosnian and Serbian fans traded ethnic chants across a court Wednesday while Bosnian-born Amer Delic held off France's Paul-Henri Mathieu in a five-set match at the Australian Open.

Delic, representing the United States, said he realized he was the middleman in what he called "a circus" but had no control over the spectators, whose noise disturbed the last two sets and affected both players' concentration.

"I couldn't control any of that, though I was trying to," said Delic, who moved to America with his parents when he was 14. "I felt bad for Paul and I apologized to him right after."

The 26-year-old from Jacksonville, Fla., rallied from two sets down to beat No. 28 Mathieu 1-6, 3-6, 6-3, 7-6 (3), 9-7 and advance to the third round.

Mathieu complained that the fans were like noisy soccer fans and were disrespectful, echoing complaints that arose after Delic's first-round match against fellow American Taylor Dent. Dent's father Phil, a former Australian player, charged that the Bosnian fans had heckled and taunted his son but Delic said they had just been supporting him.

On Wednesday, however, fans focused less on the match and more on each other, swapping slurs that Delic refused to translate. It was reported the Serbian fans entered Court 13, where Delic was playing, after a Serbian player had finished a match on a nearby court.

The tensions and enmity of the Balkan conflict have been transplanted to Australia along with the Bosnians, Serbians and Croatians who have migrated here, and they are among the most vocal fans at sporting events.

Things turned ugly at the 2007 Australian Open, when fighting broke out between Croatian and Serbian fans at Melbourne Park and more than 150 people were removed from the grounds after attacking their rivals with fists, sticks, bottles and flagpoles.

Delic realizes the high potential for disaster between fans at his next match, in which he faces defending champion Novak Djokovic — a Serbian.

"I just hope the next match with Novak doesn't turn into a World War III," he said. "I'm going to try to tell my fans that we don't need to be embarrassing ourselves in front of the world. I'm hoping Novak says something to Serbian fans, also. Leave the politics aside. It's not my fault and it's not Novak's fault. We're out here playing tennis and we need to keep it that way."

Delic said he keeps in touch with his Australian-based fans through his Web site and that he would also talk to leaders of the Bosnian community in Melbourne.

"Obviously I like those fans, they're getting me through these matches but I think today was bad," he said.

Australian Open organizers had no immediate comment on the behavior of the fans.

Victoria state police, handling security for the event, have warned spectators that the use of indecent or obscene language or threatening or insulting words are punishable offenses.

Troublemakers face penalties including arrest, ejection, fines or a ban from the Melbourne Park venue.