LUKE Moore once again proved the scourge of Peterborough to end Albion's three-game winless run and warm up a bumper Boxing Day crowd.
The former Villa striker followed up his double at London Road in August by firing a priceless opener in the 61st minute - his fourth of the season.
And Posh defender Ryan Bennett got into the festive spirit by heading the Baggies' second into his own net six minutes later.
Roberto Di Matteo's side never looked in danger against the team which started the day second-bottom but had to show real patience after struggling to find any real rhythm until the early stages of the second half.
Albion kicked off in third spot after Nottingham Forest's goalless draw at Watford in an earlier kick-off saw Billy Davies' men leapfrog them.
The Baggies also found themselves 11 points behind leaders Newcastle after the Toon's 2-2 draw at Sheffield Wednesday.
Di Matteo named an unchanged XI for Albion's first game in 12 days following last weekend's postponement at Blackpool. Opposite number Mark Cooper also stuck with the same team.
Any suggestions that English football should introduce a winter break were somewhat dispelled by The Hawthorns' biggest attendance of the season.
Such was the demand from the home hordes that the void separating the two sets of fans in the Smethwick End was moved to create as much room as possible for Baggies supporters.
Both teams took a while to settle into their stride but it was Peterborough who survived the first scare of the game.
Posh keeper Joe Lewis was relieved to see Jerome Thomas' volley from just inside the box deflect off Gabriel Zakuani and fly just wide after the visitors failed to clear a Chris Brunt corner.
Dean Kiely was called into action moments later when he pushed away George's Boyd's dangerous centre which just evaded the outstretched boot of Craig Mackail-Smith.
However, after that brief spell of goalmouth activity, the game reverted back into a scrappy affair, with both teams losing their way in the final third.
In fact, it wasn't until the 25th minute that the next effort on goal arrived, with Thomas dragging a speculative effort well wide of Lewis' right-hand post from 30 yards.
Lewis finally had a save to make on 31 when Bennett helped Simon Cox's attempted throughball into Moore's path and the striker fired a fierce shot goalwards, which the Posh No.1 gathered at the second attempt.
Albion gradually got on top, though, and almost broke the deadlock two minutes later.
Thomas' diagonal ball took a wicked deflection off a United boot and dropped neatly for Gianni Zuiverloon eight yards out, but the right-back volleyed just over Lewis' bar.
Chris Whelpdale recorded Peterborough's first shot at goal on 37 when he dragged a weak drive well wide from 30 yards.
And Boyd was even further off target three minutes later from a short free-kick.
That proved the final action of a tame first 45.
Albion upped the tempo after the break and kept Posh pegged back - but they were still well short of being at their best.
A brilliant left-wing run by Thomas got the crowd on their feet in the 55th minute and Moore came within inches of sliding the former Charlton ace's low centre into the net.
Thomas teed up the ex-England Under-21 striker again moments later but his swivel and shot was blocked in the box.
Lewis came for and missed Brunt's ensuing corner and the ball looped onto the unsuspecting Abdoulaye Meite's and bounced agonisingly over the empty net.
But a goal had been coming and it duly arrived just past the hour mark.
Graham Dorrans spearheaded a terrific counter attack by running from the edge of one box to another before threading in Moore, whose shot on the turn proved too powerful for Lewis.
Moore was at it again moments later after great persistence by Zuiverloon down the right, but his goalbound shot was blocked by sub Craig Morgan.
But the Baggies were two up on 67 - and in bizarre fashion.
There appeared to be little danger when Moore volleyed harmlessly into the ground from Brunt's cross and watched the ball loop into the penalty area.
But Posh centre-half Bennett lost his bearings under pressure from Dorrans and headed the ball past Lewis and into his own net.
Albion were now in the comfort zone but almost let Peterborough back into the game with seven minutes left when the otherwise impeccable Jonas Olsson misplaced a header to central defensive partner Meite.
Sub Shaun Batt seized the ball and broke clear, only to be denied by a wonderful Kiely block.
Just a minute later, it should have been 3-0 when Brunt slipped sub Chris Wood through. With just Lewis to beat, the New Zealand international pulled the trigger from 15 yards but his effort crept inches wide of the far post.
Albion were turning the screw now and sub Filipe Teixeira was denied by Lewis after skipping past Posh replacement Tommy Rowe.
Teixeira, who was enjoying a lively cameo, went close again on 86 when he couldn't quite stretch far enough to convert Zuiverloon's low centre with the goal gaping.
Kiely was called into action one last time when he pushed away Lee Frecklington's 25-yard pilederiver.
ALBION (4-4-2): Kiely; Zuiverloon, Meite, Olsson, Mattock; Brunt, Jara, Dorrans, Thomas (Teixeira 70); Moore (Martis 90+2), Cox (Wood 78). Subs not used: Allsop (gk), Bednar, Cech, Mulumbu.
PETERBOROUGH (4-4-2): Lewis; Bennett, Zakuani (Rowe 75), Geohaghon, Griffiths; Whelpdale (Morgan 62), Frecklington, Coutts (Batt 70), Boyd; Mackail-Smith, Mclean. Subs not used: McKeown (gk), Lee, Green, Simpson.
GOALS: ALBION - Moore (61), Bennett (own goal 67).
BOOKINGS: ALBION - Mattock (foul 68), Cox (foul 75). PETERBOROUGH - Frecklington (foul 38), Zakuani (foul 55), Morgan (foul 78).
REFEREE: M Jones (Chester).
ALBION STARMAN: Jonas Olsson.