Claudio Ranieri took a much-changed line-up to the Estadio do Dragão, handing starts to the likes of Ben Hamer, Marcin Wasilewski, Ben Chilwell, Demarai Gray and Nampalys Mendy, leaving Riyad Mahrez and Jamie Vardy at home.
There was also a Leicester debut for 18-year-old midfielder Harvey Barnes who came off the bench in the second half, but it was not really a night to remember for the Foxes.
Unbeaten before Wednesday night, Leicester found themselves a goal down after just six minutes when Andre Silva stayed down to head home Jesus Corona's corner before the Mexican winger double his side's advantage 20 minutes later with a stunning volley from Alex Telles' floated cross from the left.
The procession continued in the second half when Andre Silva dusted himself off after being fouled by Danny Drinkwater in the six-yard box, sending Hamer the wrong way from 12 yards.
With 77 minutes on the clock, Andre Silva played a lovely through ball for Diogo Jota who hammered home to complete the rout.
The result did nothing to change the Group G table with Leicester finishing on top with 13 points in their debut European campaign, with Porto second just two points behind.
2016/17 UEFA Champions League - Group G