Looking every inch promotion material, Walsall played with confidence and composure to complete a league double over a Posh side that has completely lost its way since the middle of December.
Posh, with a string of changes following Saturday's setback at Hartlepool, produced the brighter start with Gavin Strachan, making a debut on loan from 'Pool, setting up Richard Butcher to send a low drive across goal and wide of far post.
Walsall took command on 14 minutes making Posh pay the price for moments of madness by Ben Futcher. The lanky central defender floored Craig Pead with one wild challenge and then brought down Martin Butler with another.
After Futcher saw yellow, Daniel Fox stepped up to take the free-kick and sent a stunning right-footed drive soaring into the roof of the home net from 30 yards. Stand-in Posh goalkeeper Paul Rachubka never stood an earthly and he was beaten again nine minutes later when, like Fox, Chris Westwood claimed his first goal of the season.
This followed a sweeping Saddlers break from a Michael Dobson free-kick, with Fox steering the ball into the path of Westwood who netted with a left-footed volley from the edge of the penalty area.
Posh came back towards the break and Clayton Ince saved impressively from Danny Crow and Aaron Mclean. Scott Dann cleard a chance for Adam Smith off the Walsall goal-line in between these two goal efforts.
A Posh reshuffle with Smith dropping to left-back and Trevor Benjamin introduced up front brought a more competitive second half home showing with old campaigner Benjamin's physical presence giving the Walsall back line some anxious moments.
Ince had to be on his toes to bundle away a curling effort from Smith and at the other end Rachubka did well to drop on the ball and deny Walsall substitute Tony Bedeau a goal near the end.