It was left to substitute striker Iyseden Christie to break the ice. He had only been on the field a couple of minutes when he scored his match winner in the 72nd.
Peterborough had a chance of making a draw of it, but substitute Lloyd Opara shot weakly as Rochdale were hoping the referee would stop play as Christie was lying prostrate and injured in the opposing goalmouth. The whistle never came and Rochdale had a lucky escape.
In a lack-lustre first half Rochdale just about edged it, although Richard Logan had a couple of good chances to put the Posh in front but on both occasions his shooting let him down.
Rochdale were in better form in the second half and gave Peterborough more than their fair share of trouble, but they could not find a way through.
Rickie Lambert twice went close for the home side, but it began to look as if a goal-less draw was on the way until Christie turned up with the winner.
Late on Peterborough began to show a bit more spirit but they were foiled by two solid central defenders - Gareth Griffiths and Mark Jackson, who kept them at arm's length and made sure that Peterborough's opportunities were far between.
A late chance came Peterborough's way when Adam Newton got away but he shot too early and his shot was collected under the crossbar by goalkeeper Matthew Gilks.
That was as far as it went for a somewhat insipid Peterborough side, who were fighting for a play-off place but this did their chances little good. Conversely, Rochdale were desperately in need of those three points and end a long list of failures at home.