On-loan teenager David Hutton jumped off the bench to earn Martin Allen's almost-doomed men a surprise point in front of a near 10,000 crowd at London Road.
The wideman, borrowed from Tottenham for the rest of the season, struck just four minutes after his 62nd minute introduction when receiving a huge helping hand from Posh keeper Joe Lewis.
The error-prone stopper contrived to allow Hutton's cross-cum-shot squirm under his body as Posh's hopes of climbing to the League One summit disappeared.
An eighth successive victory would have sent Darren Ferguson's flyers to the head of affairs for the first time and everything appeared to be going to plan during a rain-lashed opening period.
Prolific frontman Aaron McLean saw an early shot hit both posts before offside strike partner Craig Mackail-Smith sent the rebound back against the woodwork.
McLean was also thwarted by a smart Scott Brown save before finally succeeding in breaking the deadlock nine minutes before the interval when lashing home from six yards after a Mackail-Smith delivery broke to him.
Brown again denied McLean on the stroke of half-time before Andy Lindegaard blocked a Mackail-Smith follow-up on the line during a frantic goalmouth scramble, before the half-time whistle provided a welcome relief to the visitors.
After the break a Paul Coutts drive cannoned against Mackail-Smith and bounced agonisingly wide, before disaster struck at the other end when Hutton dashed past defender Russell Martin and left Lewis red-faced.
Mackail-Smith headed a Shaun Batt cross wide at the near post as Posh failed to regain their advantage in the final quarter.
The point was enough to secure Posh a play-off place, while Cheltenham are a massive 12 points from safety.