Boss Claudio Ranieri had warned his side, the shock Premier League winners the previous season, against expecting another fairy tale – but it was a dream night in Belgium after Leicester scored twice inside the first half an hour.
Marc Albrighton netted the Foxes' first-ever Champions League goal, and first
in Europe since 2000, before Riyad Mahrez crashed in a brilliant free-kick.
Mahrez made it 3-0 with a second-half penalty to leave Leicester, who dominated at the Jan Breydel Stadium, top of Group G.
Albrighton said afterwards: "When I was a kid it is something you dream of doing, scoring in this competition. I never thought I would get the opportunity to play in this competition, let alone score.
"To play is one thing, to score is something else and it will live with me forever."
Leicester advanced from the group, which also contained Porto and Copenhagen, and went on to reach the quarter-finals – where they bowed out to Atletico Madrid.