Hundreds of Italians turned up at Anfield with tickets for parts of the ground designated for Reds fans - apparently bought from tour operators, rather than touts.
Some were ejected from the stadium and others were turned away.
But police were unable to keep them away from the minority of LFC fans who, Chief Superintendent Dave Lewis said, were intent on causing violence.
Around 40 Napoli supporters, some armed with sticks and with leather belts wrapped tightly around their knuckles, attacked a group of hooded Liverpool youths after the match.
The major flashpoint came on Walton Lane - outside Everton FC's Goodison Park.
Police vans, officers on horseback and on foot swooped to contain the chaos, eventually rounding up the Italians to stop them roaming the streets around Stanley Park.
The Walton Lane incident happened at around 11pm, shortly after the Italians with proper tickets were herded from Anfield to their coaches on Priory Road.