The pressure showed as the Foxes started the night six points adrift of second-placed Hull City. And, whilst they had the safety net of two games in hand over their rivals, a win was vital if they were to plug the growing gap that was forming at the top of the Championship.
Welcoming back Chris Wood and Ben Marshall to their starting 11, the Foxes faithful could have been forgiven for expecting a performance from their team that was worthy of their promotion-chasing credentials.
However, an almost inevitable first half goal from former Fox Yann Kermorgant - who was making his first return to Leicester since his departure in 2010 following that play-off penalty miss - and a wonder strike from substitute Danny Haynes set the tone for the evening as City suffered their second successive league defeat.
Kermorgant excelled in his role as villain and his influence was the telling factor in the visitors win.
The Foxes' nerves were showing early on and this was epitomised by Danny Drinkwater's shaky back-pass which resulted in Kermorgant's opener on 20 minutes.
Drinkwater's blind pass was intercepted by Bradley Pritchard deep in the City half and the midfielder's cross was met with a simple finish from Kermorgant.
The goal seemed to spur the Frenchman on, and his confident mood continued to trouble the City backline throughout the contest.
Whilst the Foxes enjoyed good spells of possession, they never really settled and their attacking options seemed limited - not helped by Charlton's organised and well-drilled defensive set-up.
Leicester finally did grab a deserved equaliser on 70 minutes when Chris Wood marked his return with yet another goal after some excellent work out wide by substitute Paul Gallagher.
Suddenly the Foxes looked the more likely to claim all three points as they continued to mount pressure on the Addick's defence - but the breakthrough never came.
Chris Powell has to be applauded for his bravery. After all, whilst most managers would have settled for a point, the former Foxes favourite brought on striker Danny Haynes with ten minutes to go - but even he wouldn't have expected his player to make such an instant impact.
Within a minute of joining the action, the striker connected with a flick on from Kermorgant and the ball was sent flying over Schmeichel from 25 yards out.
Leicester poured forward in an attempt to rescue a point, and will feel unlucky not have been awarded a penalty as the minutes ticked away - but Charlton survived the late onslaught to clinch an impressive away win.
The night went from bad to worse for the Foxes, as wins for Hull City, Crystal Palace and Watford meant that the Foxes will have to make up nine points on second-placed Hull if they are to realise their dream of automatic promotion.
Nigel Pearson will now turn his attention to his team's trip to Bloomfield Road where Paul Ince's Blackpool will be waiting on Saturday.