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.

Almost lost amid the drama was Serena Williams' defeat later of China's Peng Shuai 6-1, 6-4 to advance to the fourth round.

A woman was injured and two men arrested for riotous behavior when Serbian and Bosnian fans threw chairs outside Rod Laver Arena after a match between defending champ 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.

"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. ... 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 were en route to a 6-3, 6-3 victory over Japan's Ayumi Morita and Germany's Martina Muller. 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 as she lost to Russian Alisa Kleybanova 7-5, 6-7 (5), 6-2. The fifth-ranked Ivanovic, a 21-year-old Serb, lost her serve nine times.

The violence also overshadowed a match later between No. 2 Roger Federer and former No. 1 Marat Safin. The Swiss star won 6-3, 6-2, 7-6 (5).