Leon Clarke bagged a brace against Darren Ferguson's promotion chasers but it was defensive frailties which really ruled the day as the Sky Blues tasted victory for only a second time in seven League One attempts.
The visitors took the lead in the 20th minute when former City youngster Shaun Jeffers netted after the home defence had struggled to deal with a free-kick.
Coventry worked some good positions but gave the gave the ball away far too often. But they were gifted a goal just before half-time when Posh goalkeeper Bobby Olejnik fluffed a clearance, allowing Clarke to bag his first.
Yet the lead last less than a minute as the impressive Lee Tomlin pounced to fire home from Joe Murphy's parried save just before the whistle.
Clarke was not be outdone, however, and three minutes after the restart he powered home a low shot after a poor punch from Olejnik.
Both sides really went for it and it was the hosts who emerged victorious.
First, Clarke slipped Franck Moussa in with 10 minutes remaining and he coolly finished from close range.
Then in the dying seconds Posh thought they had scored but the ball was cleared down field and Callum Wilson shot home to complete a first defeat in six on the visitors.