Posh defended stoutly for 79 minutes to be fair and the hosts looked a frustrated side running quickly out of ideas.
Ten minutes later it was 3-0 and Posh had recorded a 12th defeat in 13 away games while maintaining their dreadful goals against record on road trips. Not for the first time this season the goals arrived in a cluster.
The defence shouldn’t be blamed. They resisted manfully until the late team collapse, but there is no release of pressure as Posh have so little going for them in forward areas. The ball comes straight back all the time as Posh are brushed off the ball so easily. West Brom’s stand-in goalkeeper David Button wasn’t required to make a save with the only Posh effort at goal a loopy Frankie Kent header that drifted wide from the only corner his side won all game in the 57th minute.
The 3-0 scoreline was harsh as West Brom are pedestrian with an over-reliance on set pieces, but they deserved their win. A corner forced home by a combination of Darnell Furlong and Cedric Kipre started the rout with Karlan Grant and Grady Diangana putting gloss to the scoreline as Posh panicked and lost shape at the back.
Posh boss Darren Ferguson sprang a selection surprise, not by reverting to three centre-backs for this particular team and their particular style, but in a recall for former captain Mark Beevers who appeared to be on his way out of the club.
Beevers was reunited with his regular League One centre-back Frankie Kent - neither had played since the mauling at Blackburn in November - with Ronnie Edwards placed in between them. The height and left-footedness of Beevers won him the day over Josh Knight. Kent was making his 100th Posh appearance.
Less of a surprise was a debut for on loan goalkeeper Steven Benda, while the return of striker Jonson Clarke-Harris for Sammie Szmodics made it four changes from the side humbled by Coventry at home last weekend. Jack Marriott had to be content with a place on the substitutes’ bench on his return from injury. Regular goalkeeper Dai Cornell and experienced defender Nathan Thompson were left out of the matchday squad altogether.
The Baggies fielded new signing Daryl Dike from the start and he missed the best two chances of a low key first-half.
Dike headed wide from Furlong’s precision right wing cross and then sidefooted straight at Benda after Jake Livermore’s long-range strike had deflected conveniently into his path.
Dike also headed a Matt Phillips cross over when under pressure, but for the most part Posh defended stoutly with Clarke-Harris heading many set-pieces away and Kent excellent from open play. Benda looked composed and ready to come of his line which was encouraging.
Posh offered no threat going the other way though as Button was a virtual spectator. Posh had no shots on goal and only a Siriki Dembele dribble four minutes before the break offered hope. Poor passing and decision-making were again apparent.
Both teams fielded three centre-backs and a pair of wing-backs so space was at a premium.
In the first minute of the second half Dike headed wide again and collided with Edwards forcing the Posh teenager with a concussion injury. Dike followed him off with a hamstring injury. Kent moved to the centre of the back three.
Diagana came on for Dike and immediately offered a different threat. One dribble ended with Posh scrambling the ball away and a one-two ended with a shot straight at Benda as the second-half settled into the same pattern as the first.
Knight, Kent and Norburn (twice in the same attack) delivered splendid blocks, while Benda saved comfortably at his near post from Grant.
Ferguson tried to make positive substitutions with Marriott and Szmodics both coming on at 0-0, but Clarke-Harris’s absence from a corner led to an initial contact lost and Furlong was on hand to pounce for that pressure relieving goal.
A hastily taken Posh free kick led to a loss of possession and the sight of Grant racing through on goal to score on 84 minutes. A simple pass behind Beevers on 89 minutes enabled Diangana to deliver a similar finish for 3-0.
There was a consolation in the shape of the bottom five all losing when Posh had the toughest fixture of them all.
But that really is clutching at straws.
Posh: Steven Benda, Bali Mumba, Mark Beevers, Ronnie Edwards (sub Josh Knight, 48 mins), Frankie Kent, Harrison Burrows (sub Joe Ward, 84 mins), Jack Taylor, Oliver Norburn, Jorge Grant (sub Sammie Szmodics, 68 mins), Siriki Dembele, Jonson Clarke-Harris (sub Jack Marriott, 73 mins).
Unused subs: Will Blackmore, Joe Tomlinson, Kwame Poku.
West Brom: David Button, Cedric Kipre, Kyle Bartley, Matt Clarke (sub Callum Robinson, 73 mins), Darnell Furlong, Jake Livermore, Adam Reach, Conor Townsend, Matt Phillips (sub Jayson Molumby 74 mins), Daryl Dike (sub Grady Diangana, 51 mins), Karlan Grant (sub Tom Fellows, 90 mins)..
Unused subs: Alex Palmer, Caleb Taylor, Taylor Gardner-Hickman.
Goals: Posh -
West Brom - Furlong, (79 mins), Grant (84 mins), Diangana (89 mins).
Cautions: Posh - Kent (foul)
West Brom - Molumby (foul).
Referee: Jeremy Simpson 6.