STANLEY manager John Coleman looked visibly shell shocked after the Reds conceded three goals in four minutes to make it three league defeats on the run.
The Reds should have been cruising against Posh after Ian Craney gave them a 22nd minute lead, the midfielder/striker then missed an open goal and both Sean Doherty and Andy Todd hit the bar in the first half.
"We should have been 4-0 up at half-time," said Coleman. "It should have been over."
But then Posh boss Keith Alexander put Danny Crow up front to make it a three pronged attack after the break and the Reds crumbled.
The home side had a lucky start when Michael Welch was judged to have pushed Ben Futcher in the area on 56 minutes and top scorer Trevor Benjamin made it nine goals for the season from the penalty spot.
Two minutes later and Aaron McLean burst through, had his initial shot saved by Ian Dunbavin but it was easy for Crow to poke home and make it 2-1.
The Reds were still reeling on 60 minutes when one-time Stanley target McLean held off Phil Edwards and fired home from a tight angle.
Paul Mullin then shot wide of an open goal as the Reds couldn't find the finish.
However, Craney doubled his tally on 79 minutes, curling a corner straight into the net to set up a lively finale.
But, on 88 minutes, Boro finished the Reds off when Crow scored his second after Stanley failed to clear a corner.
"We managed to snatch defeat from the jaws of victory," added Coleman. "I am so upset. Keith Alexander will never have so much luck again."