THE brawling troublemakers who yesterday marred the opening day of the Australian Open will be free to enter Melbourne Park today.Australian Open officials yesterday handed video footage of warring Serb and Croat supporters to police.

The opening day tickets of more than 150 fans were cancelled.

But Open spokesman John Lindsay conceded there would be nothing to stop the same offenders walking through the turnstiles this morning.

Serb and Croat supporters have both vowed to return to the scene of yesterday's battle to renew hostilities, though their community leaders have called for calm.

A first-round clash between Serb Ilia Bozoljac and Croat Marin Cilic on court 21 has added fuel to the incident.

Dozens of police and security are expected to surround the playing area late this afternoon.

"We will monitor them and if we feel there are any issues arising we will take the appropriate steps," Mr Lindsay said.

"Obviously we'll be keeping a close eye on everyone but we're not going to judge every fan on the basis of a few.

"It's the first time we've had an incident of this nature. We moved a large group off site."

Mr Lindsay would not say whether Croat and Serb fans would be body searched. All bags are searched at the gate.

But he said national emblems or flags would not be banned at Melbourne Park.

"Colourful fans are a key part of this tournament and have been for years," Mr Lindsay said.

"You don't judge an entire group of people on the actions of a few.

"But we do monitor flags and chants and if there are flags that aren't the recognised national flag of a country then we do step in."

Tennis Australia chief executive Steve Wood said police and security were well placed to deal with any repeat today.

Serbian and Croatian community leaders condemned the violence.

Both Father Miroslav Popovic from East Brunswick's Serbian Orthodox Holy Trinity church and Ivica Fonti, a founding member of the Australian Croatian Association in Melton and the western suburbs, called for calm.

Father Popovic said no Serb accepted the scenes.

"And it affects the players, the Serbian tennis players -- I know they are not happy with what has happened," he said.

Mr Fonti said the scars of the 1991-95 Croatian War of Independence between the Croatian government and the Serbian and Yugoslav People's Army were still very raw.

"I am calling for calm," he said.