Yann Kermorgant silenced the jeers of the Leicester fans by firing Charlton to victory over his former club.
The French striker was booed by the away support when his name was read out before kick-off.
But he struck Charlton's second goal after Bradley Wright-Phillips had opened the scoring.
Substitute Andy King pulled one back for Leicester in the second half - but it was a miserable 49th birthday for their manager Nigel Pearson.
Charlton paraded Ricardo Fuller on the pitch at half-time, having signed the former Stoke striker earlier in the day.
- Born: Vannes, France, 8 November 1981
- 2002-04: Vannes
- 2004-05: Chatellerault
- 2005-07: Grenoble
- 2007-09: Stade Reims
- 2009-11: Leicester
- 2010-11: Arles-Avignon (loan)
- 2011- : Charlton
Kermorgant left Leicester fans in agony in 2010 when he failed with an attempted chipped penalty as they lost to Cardiff in a Championship play-off semi-final shoot-out.
But he made no mistake against the Foxes when the ball fell to him in front of goal following a corner, confidently lashing it home before raising a finger to his lips in celebration.
That came after Charlton had taken the lead against the run of play in the 18th minute, when Wright-Phillips collected Bradley Pritchard's pass and turn on the edge of the penalty area to fire a superb low shot past keeper Kasper Schmeichel.
Schmeichel but smart saves to keep out Leon Cort and Wright-Phillips again, before Kermorgant struck from a Danny Hollands corner.
King pulled one back with a neat finish after being set up by fellow half-time substitute David Nugent.
Charlton keeper Ben Hamer then saved well from Lloyd Dyer twice and Anthony Knockaert before keeping out a stoppage-time header from Jamie Vardy.
Leicester City manager Nigel Pearson told BBC Radio Leicester:
"We should have won. In the first half we didn't react to turnovers quickly enough. We got caught on the counter-attack and conceded two poor goals. But in the second half, we totally bossed it and created enough opportunities to win.
"We've not taken our chances. I would say we've played some pretty good football but I'm not going to paper over cracks. The goals we conceded were soft and, ultimately, we've not taken any of our chances. We had plenty of opportunities to win a game.
"We didn't pick up enough second [phase] balls today. We didn't collectively do enough to limit their opportunities. The first goal was a poor goal. Our recovery from losing the ball was poor.
"We need a better all-round team performance. There were some very pleasing elements but there were some missed opportunities."
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