Police and Australian Open organisers are on high alert on Tuesday amid fears ethnic clashes between Serbs and Croats that marred the opening day of the Grand Slam could erupt again.

Serbia's Ilia Bozoljac and Croatian Marin Cilic were scheduled to play a first-round match later on day two and it was thought the clash could set the scene for a repeat of the soccer-style brawls that stained Melbourne Park on Monday.

However, suspension of matches due to the extreme heat policy appeared to have kept the troublemakers away from the grounds.

Despite their absence, security has been increased with fans being scanned by metal detectors as they entered the gates.

When the potential flashpoint match does take place, a cordon of heavy security is expected around the outside court after thugs had vowed to renew hostilities.

"We'll definitely be here... we're coming back," a Serbian supporter clad in his national colours was quoted as saying in Tuesday's edition of the Herald Sun newspaper.

About 150 fans were evicted from the Melbourne Park grounds on Monday after fighting flared between rival Croat and Serb supporters.

It was the first time such violence had flared in more than 100 years of Grand Slam tennis history.

Police admitted they were surprised by the scale of Monday's incident.

BOTTLES THROWN

"Certainly we have never had this sort of behaviour at the tennis before," acting superintendent Chris Duthie said in a television interview.

"I wouldn't say [we were] underdone, but we had sufficient police resources for a normal Australian Open tennis match.

"This was something out of the ordinary. I can assure you, though, that we will not have that problem again."

Police made no arrests despite the scuffles and organisers admitted that they had no way of preventing the fans from returning to the tournament.

"We will monitor them and if we feel there are any issues arising, we will take appropriate action," Open spokesman John Lindsay said.

"It's the first time we've had an incident of this nature... we're going to keep a close eye on everyone but we're not going to judge every fan on the basis of a few."

In scenes reminiscent of clashes between warring soccer fans, insults were exchanged between the rival fractions before the violence escalated to bottles being thrown, and kicks and punches being traded.