Two goals from Kevin Phillips allowed Blackpool to continue their 100% winning start to the Championship season.
Veteran striker Phillips scored a goal in either half as Ian Holloway's men moved on to six points for the season.
Peterborough's George Boyd pulled one back for the visitors eight minutes from time but the winger's effort ended up as a mere consolation.
Both sides are back in league action on Wednesday evening when Blackpool host Derby County while the Posh travel to Millwall.