MELBOURNE, Australia — A skirmish between ethnic rivals, a half-naked streaker and an upset of Ana Ivanovic combined for an extraordinary Friday at the Australian Open.

A woman was injured and two men arrested for riotous behavior when Serbian and Bosnian fans threw chairs outside Rod Laver Arena following a match between defending champion Novak Djokovic and Bosnian-born American Amer Delic.

Police said about 30 fans were ejected from Melbourne Park.

Djokovic, a 21-year-old Serb, won the spirited but good-natured match 6-2, 4-6, 6-3, 7-6 (4). But as the players hugged at the net, the first of dozens of chairs flew on the lawn near a big-screen TV showing the match.

"There's absolutely no place for that. This is a tennis match," said Delic, who moved from Bosnia at 14 and lives in Jacksonville, Fla. "As I'm sure you all saw at the end, Novak and I are friends. We're both competitors. In the end it was a fair match, and there was no reason for such things."

Earlier Friday, a streaker dashed on court while Venus and Serena Williams played doubles, prancing around before being arrested.

The Williams sisters were en route to a 6-3, 6-3 victory over Japan's Ayumi Morita and Germany's Martina Muller when the man, wearing only a shirt, sprinted across the sidelines and made several dance moves before heading toward an exit.

He was met by security guards, arrested and banned for the event. He was not immediately identified.

Ivanovic's hopes of a return trip to the final fell apart in a barrage of mistakes, losing to Alisa Kleybanova 7-5, 6-7 (5), 6-2. Ivanovic was pressured by the 19-year-old Russian's aggressive style. The fifth-ranked Ivanovic lost her serve nine times and finished with 50 unforced errors to only 23 winners.

Ivanovic, a 21-year-old Serb who has relatives in Melbourne, was appalled by the violence.

"Sport is a great thing to bring people together," she said. "I'm very sad to see these things happening."

The afternoon violence also overshadowed the night match between second-ranked Roger Federer and former No. 1 Marat Safin. The Swiss star won 6-3, 6-2, 7-6 (5).

"Terribly disappointing," Federer said of the fan conflict. "Fans, 99.9 percent of the time, are always great. Then you have some people who carry it outside of the tennis courts, lose their minds. It's unfortunate."

Tennis Australia chief executive Steve Wood released a statement saying police and security adequately handled the fan clash.

Victoria state police Inspector Chris Duthie said the fighting was allegedly sparked when one group threw a tennis ball at another. Security officers and police quelled the fight within minutes.

Two years ago, police ejected 150 people after similar violent clashes involving people of Balkan heritage at Melbourne Park.

Before finally asking reporters to change the subject, Djokovic lamented that players can't control their fans. Delic had earlier used his Web site to ask his backers, who were boisterous to the point of disruption in the qualifier's first two matches, to tone it down.

Djokovic next plays 2006 runner-up Marcos Baghdatis of Cyprus, who beat No. 23 American Mardy Fish 6-2, 6-4, 6-4. Baghdatis is unseeded and ranked 97th after playing in only 12 tournaments last year because of wrist and back injuries.

Andy Roddick had a 6-3, 6-4, 6-2 win over Fabrice Santoro, who may have played his last Australian Open. Roddick produced 22 aces against Santoro and next plays Tommy Robredo of Spain.

In other matches, No. 8 Juan Martin del Potro of Argentina extended his winning streak to seven matches, and No. 19 Marin Cilic of Croatia ousted No. 11 David Ferrer of Spain.

On the women's side, Olympic silver medalist Dinara Safina beat No. 25 Kaia Kanepi of Estonia. Fellow Russians Vera Zvonareva, seeded seventh, and No. 10 Nadia Petrova are also in the fourth round.

Federer looked dominant in pursuit of a 14th Grand Slam title that would tie Pete Sampras' record. He'd have preferred to talk more about Safin's game, likely the mercurial Russian's last at the Australian Open.

Instead, the questions went back to the fan violence.

"It's not what's supposed to happen," Federer said. "I think we set an example as players, and the fans should follow. This tournament works so hard all year long to make up a good event. I call it the 'Happy Slam.' Then you come here and you see these scenes."