Matt Spring scored the winner against his former club as Leyton Orient secured a win over 10-man Charlton.
Visiting keeper Ben Hamer was sent off for handling outside the area and replacement John Sullivan failed to reach Spring's 20-yard deflected drive.
The home side could have doubled their lead but Jimmy Smith's header was contentiously ruled out for offside.
Rhoys Wiggins almost equalised for league leaders Charlton but Ben Chorley cleared his effort off the line.
VIEWS FROM THE DRESSING ROOM
Leyton Orient manager Russell Slade told BBC London 94.9:
"It was packed with excitement I felt, a good local derby and a thoroughly deserved win.
"[On the sending off of Charlton keeper Ben Hamer] It has connected with his hands, it's whether you decide if its intentional or not. The ref is in a good position to see it and he gave it.
"I think we squandered a few opportunities and whilst it's 1-0 they are still in the game, they are not used to losing and they are going to keep going and credit to them they did keep going."
Charlton boss Chris Powell told BBC London 94.9:
"I am disappointed to lose a game in any circumstances but I feel we have been hard done by.
"First of all it was a bad decision by my keeper, but is it a goal scoring opportunity? I don't think so.
"We could have got something at the end, we could have nicked a point but I am very proud of the way they applied themselves in difficult circumstances."