Two second-half goals from Sammie Szmodics were enough for Peterborough United to edge past the Addicks at the Weston Homes Stadium.
On a poor pitch the Addicks battled and, after Conor Washington’s 13th minute penalty, looked in control, but a defensive error allowed Szmodics in for his first in the 66th minute and the midfielder confidently slid in his second 13 minutes later.
Lee Bowyer refreshed his squad making four changes but remained in the same attacking 4-4-2 formation that was so effective as the Addicks beat Bristol Rovers on Saturday.
Ian Maatsen was the first player to have a shot at goal and hit a powerful, dipping effort from 25-yards out. The ball just cleared the crossbar to the relief of Posh goalkeeper Christy Pym.
At the other end dangerman Siriki Dembele saw a blocked shot trickle towards Ben Amos.
The Addicks had the better of the opening minutes and were awarded a 13th minute penalty when Jason Pearce got in between two Peterborough defenders, trying to get on the end of Jake Forster-Caskey free kick, and was hauled to the ground. Washington calmly stepped up, finding the bottom corner with an expertly-placed penalty for his seventh goal of the season.
Paul Smyth, who had won the free kick for the Addicks’ goal, cut inside in the 20th minute but saw his left-footed effort go high and wide of the goal.
Only a poor pitch, the two sides battled for control of the midfield, with the chances in the first half few and far between.
Just before the half-time break, Omar Bogle, who worked hard throughout, turned well in the box and his cross was agonisingly ahead of Smyth sliding in at the back post.
The home side worked a nice position in stoppage time in the first half but Smyth did well to get back goalside of Dembele, eventually the ball was laid back to Jack Taylor whose shot from deep was very easy for Amos to gather.
Charlton started the second half the better of the two teams and Gunter nearly doubled the Addicks lead in the 66th minute when Bogle headed down for the right back who headed over the crossbar.
Posh went down the other end and levelled the scores with a soft goal. A miscommunication between Pearce and Deji Oshilaja allowed Szmodics through on goal and he comfortably slotted past the onrushing Amos.
The attacking midfielder got his second of the game when he calmly slotted home after getting in behind the Charlton defence after the Posh won the ball high up the pitch.
With time running out Amos came out quickly to deny Szmodics a hat-trick and the Addicks were unable to get a goal to get them back into the game.
Peterborough United: Pym, Butler, Thompson, Beevers (C), Kent, Taylor, Clarke-Harris, Dembele, Szmodics, Kanu (Burrows 58), Hamilton (Brown 64)
Subs (not used): Gyollai, Eisa, Broom, Jones, Mason
Goals: Szmodics 66, 79
Booked: Pym 13 (dissent), Ferguson 52 (dissent), Kent 65 (foul on Millar), Szmodics 85 (dissent)
Charlton: Amos; Gunter, Oshilaja, Pearce (C), Maatsen; Smyth (Gilbey 79), Pratley, Forster-Caskey (Shinnie 71), Millar (Williams 79); Bogle (Aneke 67), Washington (Schwartz 67)
Subs (not used): Harness, Matthews
Goal: Washington 14
Booked: Forster-Caskey 45+1 (foul on Beevers), Millar 51 (foul on Kent), Smyth 63 (foul on Taylor), Pratley 90 (foul on Burrows)
Referee: S Purkiss