Ayoze Perez's first goal since March and Harvey Barnes' second-half strike looked to have sent the Foxes on their way to a victory.
But Napoli striker Victor Osimhen grabbed a classy lifeline for the visitors and then headed in a late leveller, with Leicester's frustrations compounded when Wilfred Ndidi was sent off in injury time.
Scenes turned ugly shortly after the final whistle as Leicester and Napoli fans clashed in the stadium.
Police and stewards had to control a disturbance between the home and travelling fans at full time with missiles thrown between supporters.
Plastic bottles and missiles were launched, while a group of Leicester fans scrambled over safety netting to clash with Napoli supporters.
It's understood an appeal went out over the King Power's speaker system asking fans to 'respect your club' by 'moving away from the segregation line'.
It was an ugly end to an enthralling game of a football.
The two clubs started the tournament as joint favourites to lift the trophy in Seville in May and went at each other as if to prove their credentials.
Download talkSPORT Edge NOW!
Whether it's goals as they go in or the latest from your club, stay up to date with everything going on in football with breaking news, live scores and in-app betting.
Download talkSPORT Edge in the App Store here.