Although possession was evenly balanced, Posh always looked the more threatening and Aaron McLean gave a hint of what was to come hitting a shot across goal and inches wide of the far post after just three minutes.
McLean was involved again when Posh swept into the lead six minutes later, slipping the ball inside for Josh Low to fire into the roof of the Rochdale net from the edge of the penalty area. This was at the end of a five-man move started by Shwan Jalal, surprisingly preferred in goal to long-serving Mark Tyler.
Baghdad-born Jalal used his height to collect an Adam Rundle corner and covered his far post as a stretching Chris Dagnall almost reached Rundle's probing cross from the left.
A rare misdirected pass by home skipper Micah Hyde let in Dagnall before Shane Blackett came to the rescue with a precise tackle.
Posh doubled their advantage a minute before the break with McLean stabbing the ball over the line after beating keeper James Spencer to a diagonal cross from Craig Morgan.
Rochdale looked more dangerous at the start of the second period and Jalal needed two attempts to deal with a David Perkins effort and then did well to punch away a dangerous cross from Simon Ramsden.
Posh soon hit back with Chris Whelpdale and Low hitting the woodwork in quick succession before Tom Kennedy hooked the ball off the Rochdale line.
A third goal looked inevitable and it came from substitute Danny Crow with a final minute tap-in from Low's precise cross.