The Red Devils' title challenge isin danger of disintegrating before the onset of winter after acalamitous mistake from Edwin van der Sar allowed Soren Tchoyi tocomplete a staggering comeback.
Javier Hernandez and Nani appearedto have put the hosts on the road to victory with their first-halfstrikes, only for Patrice Evra's bizarre own goal to provide West Bromwith their window of opportunity.
Lack of inspiration: Substitute Wayne Rooney failed to prevent Manchester United from conceding a two-goal lead at Old Trafford
Yet the biggest story was perhapsthat Rooney sat through all the drama on the bench, the cover of injuryhe himself had removed no longer available to explain an absence thatwas the culmination of an awful six months.
Even when he came on with 19 minutesleft, it was not as a central striker, although he did have United'sbest chance of a winner, which was turned away by James Morrison.
If Rooney really was challengingFerguson's authority with his midweek revelation that he has not beensuffering from an ankle injury, there are a long list of players whocould be used as proof of who wins such battles at Manchester United.
David Beckham, Roy Keane, Jaap Stamand Ruud van Nistelrooy have all been bundled out of the club afterFerguson deemed there was no point having them around and there is noreason to presume Rooney would be any different if the manager felt heno longer had use for him.
Dropping points: Michael Carrick, Edwin van der Sar and Patrice Evra after Somen Tchoyi condems United to the third straight League draw
Today there was no obvious fitness reason for Rooney's exclusion given he completed the full 90 minutes for England.
This time, the only conclusion todraw would be poor form was the determining factor. The long-termrepercussions will be interesting to say the least.
Ferguson's decision to put DarronGibson on as Ryan Giggs' replacement when the Welshman limped off fiveminutes before the break suggested there will be no easy way back forRooney, who celebrates his 25th birthday later this month.
The United manager is far tooexperienced to require justification for any of his actions. He got itanyway on his side's first real attack.
Fighting spirit: West Bromwich Albion's Jonas Olsson (centre) celebrates after an Patrice Evra (not pictures) scores in his own net
West Brom might have been aggrievedwhen Morrison was ruled to have fouled Hernandez on the edge of thearea. Much of the punishment was self-inflicted.
Nani's dipping free-kick wasdifficult to deal with. But Scott Carson should have done far betterthan merely parry the ball into Hernandez's path.
With no defender accompanying himinto the box, the Mexican gleefully tapped home his third goal of theseason - two more than Rooney, whose only Premier League effort cameagainst West Ham in August.
The hosts wasted at least threedecent chances to double their lead, which meant that Rafael'sintervention as Chris Brunt waited to tap home Marc-Antoine Fortune'sfar-post cross was crucial in keeping their noses in front.
Relief came courtesy of Nani, whocapitalised on Nicky Shorey's untimely slip, darted to the edge of thebox, then kept going to thrash Dimitar Berbatov's astute return passinto the corner.
Through it all, Rooney remainedimpassive on the bench, wondering whether he would get a chance torestore his own confidence after an alarming slump which began with theankle injury he suffered at Bayern Munich in March.
United threatened to score again atregular intervals, although West Brom, winners at Arsenal a fortnightago, retained an attacking intent that would not pay dividends untilafter the break.
No chance: Nani (right) beats Baggies keeper Scott Carson to give United a 2-0 lead
Given all the attention that hadbeen focussed on the £27million sharpshooter, it was almost forgottenhow abysmal United's defending has been at times this season.
Two goal leads had already beenthrown away against Everton and Liverpool this season, and Fulhamgifted a late equaliser at Craven Cottage.
Yet to see United's advantage wipedout in a six-minute second-half spell was still a shock. West Brom'sfirst was bizarre and came courtesy of two deflections - off Andersonand Patrice Evra - that took a Brunt free-kick past Van der Sar at thenear post.
The second was all Van der Sar'sfault as he inexplicably dropped Brunt's steepling cross to presentTchoyi with a tap-in as unexpected as it was gleefully accepted.
This boy's a bit special: Javier Hernandez gave Manchester United the lead after just five minutes at Old Trafford
Rooney - together with Paul Scholes - were given 19 minutes to save United, although he was asked to do it from the left wing as Ferguson went for broke.
The United striker had one chance, which Morrison diverted away as West Brom clung on.
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