Charlton win with late doubleU's: Morris, Clarke, Roast, Kent. Brown, Curtis, Lapslie, Szmodics, Simmons, Blanche, Bonne
The spot kick was scored and the final whistle went with the U's suffering their first defeat of the season.
Morris was then harshly adjudged to have committed a foul and the referee pointed to the spot.
In the dying seconds, Morris tried to shepherd the ball out but a Charlton player wouldn't give up the ghost and managed to get to the ball.
A corner was cleared to the edge of the box but a fantastic strike came straight back and the scores were level.
It looked to have been a successful defensive performance, with the score still at 1-0 as the game went injury time but Charlton's perseverance paid off in the end.
The U's dealt with the onslaught, protecting keeper Morris, in for the injured Miles Palmer, well and restricting their opponents to long shots and crosses from deep.
Charlton came out for the second half and increased the direct nature of their play, pinning the U's back for long periods with long balls pumped into the U's penalty area.
He made amends just before the break though, as he latched onto a near post cross from Macauley Bonne to score the opener.
Jack Curtis should have scored as he went one on one with the keeper but his effort went wide of the post.
Despite the different challenge, the U's youngsters dealt well with everything Charlton threw at them and managed to create chances at the other end.
The game started at a high tempo, with both teams pressing high up the pitch and Charlton employing far more direct tactics than the U's previous opponents, Bristol City and Swansea.
It was a cruel end for keeper Joe Morris, from the U's U16s squad, as he had no chance with the first and was harstly adjudged to have fouled the Charlton forward to concede the penalty.
First, a fantastic strike got the Addicks an equaliser before a penalty sealed things with the last kick of the match.
As the clock moved past ninety minutes, they were still leading but two injury time strikes gave Charlton the win.
Tony Humes' youngsters had led at half time, thanks to Jack Curtis' near post finish.
The U's U18s were beaten 2-1 by Charlton, by a late double denying them the points.