Wayne Purser, plucked from non-league Hornchurch earlier in the month made it two goals in as many Posh games when he opened the scoring on 37 minutes, side-footing in a blistering low cross by David Farrell at the near post.
The goal was all that separated the sides at the half way stage, although Purser also saw a looping header snatched from beneath the crossbar by Vale's Jon Brain and the 24-year-old put another effort narrowly wide following Adam Newton's accurate centre.
Vale had their chances with George Pilkington bringing a fine early save from Mark Tyler and, after previously failing to hit the target from a great position, Billy Paynter almost made amends with a shot from point blank range that Tyler did spectacularly well to push away one handed.
Posh were again exposed immediately after the break with Nathan Lowndes going clean through only to scuff his shot wide, although Vale were soon made to pay for their poor finishing as the home side took command with a two goals in nine minutes burst.
Farrell punished slack marking hit Posh's second after 61 minutes, converting a cleverly taken free-kick by skipper Curtis Woodhouse with a cracking left-footed shot into the roof of the net, and the 70th minute brought a fine solo break by Andre Bouchard who gave Brain no chance slotting in goal number three.
Woodhouse hit the fourth from the penalty spot with seven minutes left after Purser was tripped, and in the dying seconds Leon Constantine was close to marking his return from a month on loan at Torquay with a goal.