Posh were on the ropes after six minutes, on the canvas after 15 minutes and knocked out of the FA Cup 10 minutes after the break. Even the official attendance made pre-match predictions of a full house look hopelessly misguided, unless of course 2,000 fans bought tickets but didn't come to the game.

If they did they showed remarkable foresight as Posh weren't able to compete against the power and craft of Championship leaders West Brom. No disgrace in that, except Posh is currently a club built on hype and wild optimism, leading to ideas well above their station.

The visitors scored two early, scrappy goals and added a third from the penalty spot before the hour mark when Craig Morgan's ankle tap on Jonathan Greening also earned him a red card. That, rather than the result, will prove to be the most damaging moment of a one-sided game, given the alarming defending of this Posh team.

Morgan is no Bobby Moore, but he represents calm amid the panic. The foul which led to his dismissal was soft, but correctly punished as in this case it's the law rather than the referee who's the ass.

Match official Jonathan Moss was far more culpable in failing to spot Martin Albrechtson's arm stop Craig Mackail-Smith's header reaching the goal midway through the first half, although Posh were 2-0 down by then against a team who rarely needed to reach full speed.

Posh had been on the attack for most of the opening five minutes, but a half-hearted attempt to play offside enabled Craig Beattie to scuff a shot across goal for Roman Bednar to tap in at the far post.

Robert Koren quickly added a second following a quick break out of defence and after Posh keeper Joe Lewis had brilliantly tipped a James Morrison shot onto a post.

And from there it was largely a stroll. Charlie Lee's free-kick was tipped over by visiting keeper Dean Kiely and from the corner Morgan's volley was headed off the line by Paul Robinson before excellence from George Boyd led to Mackail-Smith's penalty shout – all worthy efforts, but one suspects a goal would have led to a change of gear from West Brom.

From the moment the teams ran on to the pitch, Posh looked to be up against it. They appeared to be conceding six inches and a couple of stone a man which naturally led to the frustrating sight of Aaron Mclean and Mackail-Smith regularly competing for high balls they had no chance of winning.

Some did improve their reputation with Chris Whelpdale's hard work and Boyd's occasional flash of inspiration, just giving way to the all-round ability of Lee in the race for man-of-the-match honours.

Lee even spent the final half-an-hour looking good at centre-back in place of Morgan. Substitute Kevin Phillips had inevitably dispatched the spot kick to complete the scoring.

West Brom could have had other goals with Filipe Teixeira missing badly with his head in first-half injury time and Beattie adding to his reputation for clumsiness by scuffing badly when well placed midway through the second half.

It was always going to be a tall order for a defence that leaked two goals against a pub side like Accrington in their previous outing to keep out a Premier League side in waiting and Posh really pinned their hopes on a decent day in front of Kiely's goal.

But the veteran number one, who is keeping former Posh prospect Luke Steele on the substitutes' bench, remains a top keeper.

He made a spectacular save to deny Mclean on 55 minutes and he was agile enough to keep out Dean Keates' header 20 minutes from time.

Of course both sides have much more realistic targets than the FA Cup, but as West Brom travel up to Preston tomorrow full of confidence, Posh will be licking their wounds ahead of a mighty match against League Two promotion rivals Rotherham.

This has been an entertaining cup run with no need for recriminations at the end of it. They will only arrive if Posh fail to win promotion.