The damage was done inside the opening half-hour as North End's on-loan shot-stopper Declan Rudd was left with egg on his face.
Tyrone Barnett gratefully gobbled up a simple chance to put Posh ahead with his sixth goal of the season after Rudd had spilled a ninth-minute shot from Grant McCann into his path.
And even worse was to follow for Rudd as he allowed a 29th-minute McCann drive from 25 yards to slip through his hands and into the net.
Rudd did in part redeem himself with stunning saves from Paul Taylor and Barnett in the same attack later in the first half, but two goals were enough to earn Posh a fourth successive victory.
Preston did threaten a revival in the second period when Bailey Wright smashed a volley against the bar while Bobby Olejnik made smart saves to keep out substitutes Nicky Wroe and Joe Garner.