Lukas Jutkiewicz denied Charlton manager Lee Bowyer a winning return to St Andrew's as Birmingham grabbed a late equaliser to earn a 1-1 draw.
Jutkiewicz's leveller in the third minute of time added on denied relegation-threatened Charlton, who looked set to win courtesy of Macauley Bonne's 58th-minute goal.
Bowyer remains the bookies' favourite to become Blues' next manager and he was four minutes of time added on from a winning first trip back to the club where he made 94 appearances from 2009-11 and won the League Cup in 2011.
Bonne's 10th of the season ended the Addicks' three-match losing run.
Blues have gone 12 games without a win but at least they avoided a fifth consecutive loss after the premature exit of head coach Pep Clotet a week ago. They have taken just seven points out of the last 36 available.
But they only had themselves to blame after Scott Hogan missed a 34th-minute penalty and blazed over the rebound, while they wasted two early chances.
Blues, in their second outing under caretaker bosses Craig Gardner and Steve Spooner, started really well and created two excellent chances in the opening minutes.
Dan Crowley robbed Alfie Doughty but his angled effort was superbly blocked by goalkeeper Dillon Phillips, then Jeremie Bela's first-time effort whistled just wide from just inside the box.
Charlton's response saw Jonny Williams fail to connect with Josh Cullen's cross after getting ahead of Maxime Colin.
Blues missed the chance to take the lead when Hogan struck a penalty straight at the legs of Phillips then ballooned over the follow-up with the goal at his mercy.
Phillips had atoned after conceding the spot-kick when he brought down Jutkiewicz, who had been left clean through when Ivan Sunjic pressured Cullen into a poor back pass.
Crowley had a half-chance in first-half time added on but sliced an angled drive off target from the edge of the box.
Hogan had another opportunity after the break but after a surging run, his angled shot diverted off the sliding Thomas Lockyer, with Bela's resulting corner palmed away by Phillips on the line.
Charlton took the lead against the run of play when Bonne tapped home from three yards after a determined run and cross by Doughty.
Phillips made a superb save to deny Blues an equaliser in the 64th minute when he tipped away Sunjic's low first-time volley through a crowd of players.
Aiden McGeady went desperately close to sealing the points for Charlton after 69 minutes.
The former Celtic winger hit the base of the post after cutting in from the right in a jinking run, then saw his follow-up smothered by goalkeeper Lee Camp.
Jutkiewicz equalised for Blues as he tapped home when Gary Gardner's shot had been palmed away by Phillips after substitute Jude Bellingham crossed, for a career-best 15th goal of the season.
What the managers said...
Birmingham's interim boss Steve Spooner: "I could not praise the players highly enough. We spoke about application and ability and the way they took on information, they displayed it.
"We had a chat and went back to basics and that's what we did. Right from the kick-off I was very impressed with us in the first 20 minutes and we made it very uncomfortable for them."
Charlton's Lee Bowyer: "For me, 49 points is safe. Looking at what the other teams down there have got to play, I think we would have been safe. It hurts a lot. But we could not see the game out. The whole team has to manage the game better.
"I feel like I'm saying the same thing again and again - we should have won this game comfortably - we hit the post and there were clear chances for three or four others. But if you miss things like that you don't deserve to win. If you don't take chances you don't score, and if you don't score, you don't stay up."