Record signing Islam Slimani scored the only goal of the game in the first half to continue the Foxes' fairytale in their first ever Champions League home game.
The party atmosphere inside the King Power Stadium was almost soured inside three minutes when Kasper Schmeichel, back in the side after three games out, found himself in no-man's land having come off his line to meet Otavio's long ball forward. Porto top scorer Andre Silva beat the stranded shot-stopper to the ball, but his potshot towards goal dropped narrowly wide of the open net.
It was Iker Casillas's turn to find himself out of position next when the Spaniard tried to punch a long Christian Fuchs throw clear, but he got nowhere near the ball and needed Felipe to glance it narrowly past the post.
Casillas would have been most concerned by the threat of Slimani heading into the match having conceded five goals to the Algerian already this year, and the former Sporting Lisbon attacker came close to adding to that tally when his glancing header was kept out by the keeper.
Slimani would prove to be the scourge of Porto once again, though, as he opened the scoring in the 25th minute by nodding compatriot Riyad Mahrez's cross home for the first ever Champions League goal at the King Power.
It was Slimani's third headed goal in his last two home appearances for the Foxes, and his sixth goal in just four meetings with Porto this calendar year.
The visitors struggled to create any clear chances from open play in response, but did come close with a free kick 10 minutes before the interval when Miguel Layun rippled the side-netting from 25 yards.
The King Power's first 45 minutes of top-level European football ended with the hosts in front, though, and they showed little sign of surrendering their advantage in the early stages of the second half as the match continued to be broken up by niggly fouls.
It was the home side who had the first meaningful opening of the second half when a flowing move saw the ball teed up for Mahrez, but his low mis-hit shot was easily turned behind by Casillas.
Schmeichel was helpless with just seven minutes remaining after clattering into Robert Huth with both players going for the same ball, but the woodwork came to Leicester's rescue as Jesus Corona's thumping first-time volley crashed against the post via a slight deflection off Marc Albrighton.
That proved to be the final major scare for the hosts, though, as they held on for an historic victory over the two-time European champions to maintain their spot at the top of Group G with six points from a possible six.
Porto, meanwhile, remain on just one point and are now winless in 17 visits to England in European competition, losing 15 of those.