Foreign news agencies have reported that 150 troublemakers were evicted from the grounds after fighting broke out between Serbian and Croatian fans.
Officials quoted witness reports that said the trouble began after Serbs shouted abuse at Croatians watching their player Mario Ancic's match on a nearby court.
Forty police and security staff rushed in "to separate the stick-brandishing, flag-waving groups, who were hurling bottles and cups of beer at each other in the Garden Square precinct at Melbourne Park," the dpa news agency reported.
Police sought to play down the incident, saying they moved quickly to isolate the ringleaders. They said no arrests were made, according to the Reuters news agency.
"They were mostly Serbians ejected as they were upsetting the Croatians," Victoria state police spokeswoman Katherine Jess was quoted by Reuters as saying.
"Police are now meeting with Tennis Australia officials to work out the next move," she said.
Croatian fourth-seeded Ivan Ljubicic was ousted by American Mardy Fish (4-6, 7-6, 6-4, 6-4) on Day One.
Another Croatian, ninth-seeded Mario Ancic, beat Japanese Go Soeda (6-4, 6-3, 6-2).
Juergen Melzer of Austria beat Ivo Karlovic (Croatia) 6-4 6-4 7-6(6).