Gareth McAuley’s poor defensive clearance was diverted past Ben Foster to give the hosts a nine-minute lead, with second-half substitute Robin van Persie wrapping up in the win at the death.
Danny Welbeck replaced Robin van Persie in United’s starting lineup, while Shinji Kagawa returned to action for the first time since October after recovering from a knee injury. The recently recalled loanee midfielder George Thorne was handed only his second-ever league start for West Brom in one of seven changes by Steve Clarke.
With United conceding the first goal in 11 of its 19 Premier League games this season, Sir Alex Ferguson would have been relieved to be afforded a helping hand after just nine minutes when McAuley diverted Ashley Young’s dive across goal through the legs of his own goalkeeper to give the league leaders an early lead.
The hosts were dominating proceedings, with the own goal only serving to add further confidence to a slick first-half display.
However, Sir Alex has often bemoaned his side’s inability to convert scoring opportunities, and was proven right to urge caution after seeing Manchester City win the title on goal difference last season, and will have been cursing his side’s luck after seeing his side’s twice thwarted when in good positions.
First, Foster showed great reactions to tip Young’s fierce drive from 16 yards onto the crossbar and away before, from the resulting corner, Michael Carrick his side-footed shot towards the far bottom corner punted off the line with the goalkeeper beaten to keep the deficit down to just one goal at the halftime break.
West Brom started the second period with a renewed passion after a largely anonymous opening 45 minutes, with Chris Brunt combining well with Shane Long and Billy Jones before test David de Gea from 30 yards within the opening five minutes.
Graham Dorrans then went close attempting to advantage of panic in the United area following a badly defended free kick from deep, but Nemanja Vidic threw his body in the way of the ball to divert the danger.
United was evidently getting nervous, and retreating from their thoroughly attack-minded first-half display, while away side were cautious to pile too many forward and leave themselves vulnerable on the counterattack.
This hesitance resulted in sporadic chances in a less-vibrant second half for the home side then than showing before the break, as the visitors grew in confidence.
McAuley nearly made amends for his own goal when he out-jumped Chris Smalling to power a header onto the United crossbar, only for the referee to penalize the 33-year-old for a foul on the defender.
As the game entered the final 10 minutes, substitute Van Persie was denied by Foster to cut the result beyond doubt for his side, the Dutchman only able to find the goalkeeper’s legs after Patrice Evra played him behind the West Brom defense.
But Van Persie did grab his almost customary goal in the 90th minute, picking up the ball on the edge of the area after a United corner was header away and curling it with ease past the impressive Foster to seal the win.