Wilfred Ndidi's deflected late leveller denied West Ham what would have been a hard fought win, after playing more than half the game with ten men.
Fabian Balbuena's first goal for the club gave the Hammers the lead after half an hour, and they held on until Ndidi's strike a minute from time, despite having captain Mark Noble sent off before the interval.
Javier Hernandez was brought into the West Ham side in place of Marko Arnautovic, who was ruled out through injury, while youngster Grady Diangana was once again preferred to Michail Antonio as deputy for long-term absentee Andriy Yarmolenko.
Claude Puel made the bold call to drop star striker Jamie Vardy, and the man leading the line in his place, Kelechi Iheanacho, had the ball in the net after less than two minutes, only to see his effort correctly ruled out for offside.
As they had at Arsenal on Monday, Puel's side started brightly, but it was the Hammers who found the breakthrough, as Balbuena tucked away after his own header had struck the post and Leicester had been slow to react.
Leicester looked sluggish, but were given a route back into the game when Noble was sent off for a late, high tackle on Wilfried Ndidi.
Vicente Iborra almost found an equaliser immediately, heading James Maddison's free-kick straight at Lukasz Fabianski.
Puel threw on Jamie Vardy for Rachid Ghezzal at the break, as the home side looked to take advantage of the extra man.
Marc Albrighton tested Fabianski with a back post volley, before Vardy missed a glorious chance to equalise, heading over when unmarked at the near post.
Harry Maguire then hit the bar with a header from a corner and as the home crowd grew frustrated and Puel was forced to roll the dice and throw on Demarai Gray and Shinji Okazaki.
But it was Ndidi who found a way through, with a strike that took a wicked deflection off Balbuena to beat Fabianski.
