Chris Hughton's men came from behind to see off their rock-bottom hosts thanks to a flurry of three goals in the space of 15 minutes either side of the interval.
However, results elsewhere delayed the inevitable at both ends of the standings.
Newcastle will have to wait until at least Easter Monday to clinch a ticket back to the top-flight and the same applies to Posh's inevitable relegation back to League One after a season to forget at Championship level.
But that didn't stop them giving the mighty Magpies a real run for their money.
Buoyed by a Carling Cup victory over a weakened Newcastle side earlier in the season, Jim Gannon's men set about completing a double success and soon hit the front.
Dominic Green broke the deadlock with a classy 20-yard finish in the 11th minute after Magpies keeper Steve Harper had charged from his area only to collide with defender Fabricio Coloccini.
Only some errant finishing from Sergio Torres prevented Posh from doubling their lead moments later.
They held onto their single-goal advantage until stoppage time at the end of the opening period when Kevin Noland dashed into the box to convert a Jose Enrique cross from close range.
And the visitors only needed three minutes after the interval to hit the front courtesy of a splendid set-piece.
Joey Barton made Posh defender Gaby Zakuani pay for a foul on Shola Ameobi by sublimely curling his first goal of the season, before Ameobi turned goalscorer to complete the turnaround just before the hour when his low drive bobbled past Posh keeper Joe Lewis.
But the bottom side refused to roll over and continued to apply the pressure with Liam Dickinson halving their arrears 14 minutes from time when Harper failed to hold onto his effort following an Exodus Geohaghon long throw.
Dickinson was then the provider when Lee Frecklington nodded a decent opportunity over shortly after, before Tommy Rowe saw last-gasp penalty appeals ignored by referee Mark Haywood.