Hundreds of Millwall fans were escorted to Brighton station by police in riot gear after last night's match against the Albion.
About 50 officers and dog handlers escorted 500 fans from Withdean Stadium down London Road after the game.
Speaking after the match, Inspector Mark Powles said: "We want to try to get the fans down to the station and out of the county.
"If we don't they will splinter into groups and could go into Brighton."
Millwall supporters, who watched their team beat Albion by two goals to one, were kept in the stadium at the end of the game as home fans left.
Scuffles had broken out before the 7.45pm kick-off when a group of Millwall fans turned up without tickets and tried to get into the stadium.
Insp Powles said: "It seems there was also some confrontation between rival supporters within the stadium."
He said police had made a number of arrests but could not say how many.
By 11pm the police operation had been scaled down after most of the fans took trains leaving Brighton.
One Brighton fan was arrested inside the ground but later released without charge.
Superintendent Paul Pearce said: "We had more officers on duty because of intelligence reports and there were 550 Millwall fans at the game, but all went pretty well."
Albion chief executive Martin Perry said: "It was quite a difficult and sensitive situation but preliminary reports suggest it all went quite peacefully and was dealt with very well."
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