Violence erupts at Oz Open

Police arrested two men and ejected another 30 people from the grounds after the rival supporters began throwing chairs and trading punches and kicks.

One woman was knocked out after being hit on the head by a chair although police later said she had not been seriously injured.

The fighting began in a garden outside the main centre court arena then flared up again outside Melbourne Park.

Inspector Chris Duthie said two men had been charged with riotous behaviour and discharging a missile while another man had been fined on the spot.

"The matter was dealt with very quickly and effectively by the police and we expect no more problems," Duthie said.

"We have a very effective police presence here. You can't stop everything happening but we will make sure this sort of thing doesn't happen."

The Australian Open has been marred by a series of violent clashes since 150 Croat and Serb fans first began brawling at the event two years ago.

Two people were evicted on Wednesday after scuffling at a bar following a match between Croatia's Marin Cilic and Janko Tipsarevic of Serbia.

There was a heavy police presence at Friday's centre court match between Djokovic, the defending champion from Serbia, and Delic, who plays for the US but was born in Bosnia.

Delic posted a plea on his website before the match pleading for fans to behave and said he was disappointed when told about the fighting.

"I'm really sad to hear about that," he said. "As I said a couple days ago, there's absolutely no place for that here. This is a tennis match."

* Around 150 fans were evicted from Melbourne Park on the opening day of the 2007 tournament after vicious fighting flared between rival Croat and Serb supporters. The fans attacked each other with bottles and flagpoles. Police were caught on the back foot because it was the first time such violence had flared in more than 100 years of Grand Slam tennis.

* In 2008, fans of Greek descent were subdued by police pepper spray after trouble erupted during a match between Fernando Gonzalez of Chile and Konstantinos Economidis, a Greek qualifier on Margaret Court Arena. The match had to be stopped for 10 minutes as the fans were removed from the stadium by police.

* Former finalist Phil Dent warned at the 2009 tournament that disruptive fans with ethnic ties at the Open were certain to cause a riot unless there was a security crackdown. Dent was outraged at the behaviour of teenage fans supporting the Bosnian-born American Amer Delic in the first-round match against his American son Taylor. "I've got to tell you their behaviour would not be accepted anywhere in the world," Dent told local radio.

* In 2009 police escorted at least five fans from Melbourne Park after narrowly averting an all-out brawl. Security moved in after tensions had boiled over in the match between Croatian Marin Cilic and Serbian Janko Tipsarevic. Punches were later thrown in a scuffle near a packed bar.

* Ethnic tension burst into violent crowd scenes after Serb Novak Djokovic's third-round win against Bosnian-born Delic. Groups of rival fans hurled chairs at each other in the beer garden outside centre court when simmering tension boiled over under the hot Melbourne sun. One woman was knocked cold when a chair struck her head. Police arrested two men and ejected another 30 people from the grounds.