Captain Peter Clarke grabbed a deserved equaliser in the final 10 minutes of the game to earn Oldham Athletic a point at the Valley.
The central defender rose highest from a Paul Green free kick on 83 minutes to level the scores in a game Latics dominated.
They did, however, fall behind on 22 minutes against the run of play as Josh Magennis gave the home side the lead with a low drive past Connor Ripley.
Athletic could have won the game in the final few minutes with substitute Lee Erwin going close but Stephen Robinson’s men had to settle for a point on the road.
The gaffer hinted at changes in his pre-match press conference and made six changes to the team which faced Swindon Town on Saturday.
Cameron Dummigan came in for his debut since returning on a permanent deal and started the game well, looking composed on the ball.
He provided a cross on eight minutes which was towards Freddie Ladapo, who was one of the five to keep his place, but it was just over the head of the Crystal Palace loanee.
Minutes later, Ladapo controlled and looked to thread the ball through to Ryan Flynn but he slightly overhit the ball and it rolled through to the goalkeeper.
Charlton striker Magennis had the first shot of the game which goalkeeper Ripley saved well, whilst a minute later, Morgan Fox rifled a free kick well over the crossbar.
Latics were much the better side in the opening exchanges and it was their high energy pressing which were causing the home side into errors, something which frustrated the Addicks supporters.
With Athletic in full control of the game, they almost took the lead on 18 minutes as Jamie Reckord’s cross found Billy Mckay but his shot was well saved by Declan Rudd.
However, Latics were hit by a sucker punch as Charlton Athletic took the lead midway through the first half.
Ricky Holmes advanced onto the edge of the area and released Magennis who was forced wide, however the striker managed to find a gap past Ripley and he gave the Addicks the lead.
Despite falling behind, Latics still took the game to their opponents and should have been level on the half hour mark.
A superb move started by Flynn saw him find Green on the left hand side. His low cross found Ladapo in the centre but the goalkeeper saved his effort from six yards.
Ryan McLaughlin fired over from 30 yards with five minutes of the first half whilst two minutes later, there were huge shouts for a penalty.
Reckord delivered the ball into the box and found Ladapo. The striker turned his man and tumbled in the area but the referee waved away the protests.
Latics continued to press after the half time break and went close to levelling early into the half.
After good work by Dummigan on the right, he found Ladapo in space in the penalty area but the striker dragged his shot wide of Rudd’s goal.
The home side went close soon after through Magennis as he fired over from close range before both side made changes.
Charlton introduced Kevin Foley and Ademola Lookman into the game whilst Robinson brought on Lee Erwin in place of Freddie Ladapo.
It would be the striker who made an instant impact on the game and could have equalised two minutes after his arrival on the pitch.
Green’s corner into the box was aimed towards the onrushing forward but he could not connect properly with his header as Charlton cleared.
Erwin again had a chance as Mckay played the ball into his path but he could not finish from close range as Latics continued to press for the equaliser.
With Latics continuing to drive forward, they did find an equaliser on 83 minutes through central defender Clarke.
The captain rose highest from a Green free kick into the box and he headed into the bottom corner to level the scores.
Athletic had to be wary a minute later as Lookman was allowed space 25 yards from goal but his fierce strike rebounded off the crossbar.
Despite that effort, Latics still looked the more likelier of the two sides to grab the winning goal as Mckay laid the ball into the path of Erwin but his effort was blocked from 20 yards.
Deep into additional time, Osei received the ball inside the penalty box, turned his man but could not get a strike away as referee blew time on the pulsating encounter.
Charlton Athletic: Rudd, Jackson (Lookman 62’), Bauer, Crofts (Foley 63’), Magennis, Holmes, Konsa, Ulvestad, Solly, Fox, Novak (Ajose 87’).
Subs not used: Phillips, Chicksen, Johnson, Botaka.
Oldham Athletic: Ripley, Dummigan, Clarke, Burgess, Reckord, Flynn, Fane, Green, McLaughlin (Osei 72’), Mckay, Ladapo (Erwin 63’).
Subs not used: Kettings, Law, Klok, Banks, Dunne.
Goals: Charlton Athletic (Magennis 22’) 1-1 Oldham Athletic (Clarke 83’)
Attendance: 8,745 (185 visiting supporters)