A late header from a corner condemned Posh to a 2-1 defeat at The Valley as in-form Charlton Athletic continued their recent good run.
It was a tale of two red cards at The Valley - one given, one not. Defender Emmanuel Fernandez was dismissed following a reckless tackle on the touchline by referee Lee Swabey, which in truth isn't really up for debate, but the foul by Kayne Ramsay on Ricky-Jade Jones for the Posh spot-kick only yielded a yellow card, when there was no real attempt to play the ball inside the box.
Manager Darren Ferguson was disappointed with that decision, so much so he ended up getting a yellow card himself for his protests, and despite a much improved resilient display, particularly with 10-men, Posh were ultimately undone a minute from time when Macaulay Gillesphey met an out-swinging corner to find the bottom corner with a header - a set-piece goal conceded again, described post-match as an Achilles Heel.
Posh actually started the contest brightly with Ricky-Jade Jones testing the goalkeeper with a couple of attempts from acute angles.
Gustav Lindgren could have done better with a one-on-one with the defender after a good pass from Mahamadou Susoho but the chance was snuffed out.
Charlton grew into the game with Luke Berry twice testing Jed Steer, who also saved brilliantly from Matt Godden from close-range.
Berry struck the inside of the post with an effort from the edge of the box with Godden poking the rebound wide of the target.
Lindgren was forced off with a shoulder injury with Malik Mothersille his replacement and he looked lively in the early moments.
Charlton opened the scoring from the spot after Sam Hughes was adjudged to have handed in the area with GODDEN firing the spot-kick past Steer.
Three minutes after the goal, Fernandez was dismissed for a challenge on the touch-line, but moments later Posh were level as MOTHERSILLE converted from the spot after Jones was felled by Ramsay.
With 10-men, Posh defended resolutely with Charlton going long following their substitutions with Leaburn and Aneke sent on to deal with the long balls.
They got their reward from a set-piece, GILLESPHEY heading home into the bottom corner from around 10-yards. Hector Kyprianou had the final chance for Posh but he diverted his effort wide under pressure.
Charlton: Maynard-Brewer, Ramsay, Gillesphy, Jones, Coventry, Campbell (sub Mitchell 90min), Berry (sub Gilbert 78min), Docherty, Edwards (sub Leaburn 71min), Godden (sub Aneke 78min), Small. Unused subs: Mannion, Anderson, Kanu.
Posh: Steer, Johnston, Wallin, Fernandez, Hughes, Edun, Kyprianou, Susoho (sub Odoh 77min), Collins, Jones, Lindgren (sub Mothersille 40min). Unused subs: Bilokapic, De Havilland, Conn-Clarke, Dornelly, Hayes.
Half-time: Charlton Athletic 0-0 Peterborough United
Full-time: Charlton Athletic 2-1 Peterborough United
Attendance: 11,653 (714 Posh fans)
Referee: Lee Swabey