A long-range effort from Reuben Duncan followed by a poacher's finish from George Alexander saw Charlton's U23s come away empty-handed on a breezy Monday afternoon in Dartford.
With the Addicks eager to return to winning ways following their defeat against Ipswich Town last week, Jason Euell’s side came out of the traps flying and looked threatening in possession.
But soon after the frantic early exchanges, the occasion of the derby began to show through with full-blooded challenges flying in from both sides.
Millwall were pressing high and were doing well to keep Charlton within their own half and it was the visitors who were the first to have a real sniff on goal when Tyler Burey displayed his pace before firing a well struck effort which Ashley Maynard-Brewer did well to palm away.
The Addicks were struggling to form any real opportunities leaving Millwall stopper Frank Fielding with little to do with half an hour played.
It looked as though Charlton had done enough to see themselves to the interval at 0-0 until Reuben Duncan picked up the ball from distance and looped a well-weighted effort over Maynard-Brewer and into the net.
After the restart, Euell's boys looked slightly more composed and began to form forays into the Lions’ half. Junior Quitirna came close to levelling the scores with a free kick on the edge of the area but his effort whizzed just above the crossbar.
Millwall continued to push for a second, forcing a good save from Maynard-Brewer before slamming over the rebound on the hour mark.
But their determination finally paid off five minutes later when the ball fell kindly to George Alexander in the box and he was able to swivel and smash the ball into the net to make it 2-0.
Both sides continued to push, the hosts looking for a foothold back into the game, the visitors looking for a goal to kill the game off. As time ticked on it looked as though there would be at least one more goal in the game.
Charlton continued to search for a goal but were unable to unlock Millwall's defence who maintained their composure to see the game out for the win.
Charlton: Maynard-Brewer, Yao, Stevenson, Maloney (Clayden 45), Vennings, Morgan (Odoh 65), Isiaka, Wiredu (Powell 75), Quitirna
Subs (Not Used): Osaghae, Ocran
Booked: Morgan 7, Maloney 44, Yao 65
(Photos: Tom West)