Wycombe Wanderers substitute Gavin Holligan poached a late London Road winner and plunged Peterborough United into deeper trouble at the wrong end of the Division Two table.
Desperately needing points distance themselves from the relegation dogfight, Posh looked to be on course for at least a draw after Andy Clarke rescued them with his 16th goal of the season.
But it was not to be and Darren Currie, impressive all night in the Wycombe midfield, provided the prefect low cross for Holligan to lash into the roof of the net.
Even before taking the lead on 37 minutes Wycombe's frontmen squandered openings following two atrocious back-passes from Posh's Mark Arber.
First, Jermaine McSporran failed to get a shot on target at all and while Johnny Dixon did a lot better, home goalkeeper Mark Tyler was equal to the challenge.
But even Tyler was left in no-man's land when Currie sent over a towering corner and centre-back Mark Rogers out-jumped every one to score with a firm header from the far post.
By then Posh had lost skipper Simon Rea through injury and manager Barry Fry had no hesitation in giving a first taste of league action to 18-year-old Sean St Ledger, who quickly settled in at the back and played with assurance far beyond his years.
Wing-back Gareth Jelleyman's aggression on the left helped Posh seize the attacking initiative and after the Welshman's 43rd minute shot was parried by Frank Talia, the Wycombe goalkeeper was powerless as Clarke helped himself to level the scores from no more than six yards.
After the break Dixon was close to restoring Wycombe's lead with a fierce shot against the angle of post and bar but Posh had more chances leaving Fry to reflect on what might have been: "Wycombe's pace killed us but it was a cruel blow to get nothing from a game that I thought was there to be won," said the Posh boss.