Sir Alex Ferguson dumped Wayne Rooney to the bench, then saw his side throw away another two-goal lead against Albion on Saturday.
The Red Devils' title challenge is in danger of disintegrating before the onset of winter after a calamitous mistake from van der Sar allowed Somen Tchoyi to complete a staggering comeback.
Javier Hernandez and Nani appeared to have put the hosts on the road to victory with their first-half strikes, only for Patrice Evra's bizarre own goal to provide West Brom with their window of opportunity.
Yet the biggest story was perhaps that Rooney sat through all the drama on the bench, the cover of injury he himself had removed no longer available to explain an absence that was the culmination of an awful six months.
Even when he came on with 19 minutes left, it was not as a central striker, although he did have United's best chance of a winner, which was turned away by James Morrison.
If Rooney really was challenging Ferguson's authority with his midweek revelation that he has not been suffering from an ankle injury, there are a long list of players who could be used as proof of who wins such battles at Manchester United.
David Beckham, Roy Keane, Jaap Stam and Ruud van Nistelrooy have all been bundled out of the club after Ferguson deemed there was no point having them around and there is no reason to presume Rooney would be any different if the manager felt he no longer had use for him.
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 to draw would be poor form was the determining factor.
The long-term repercussions will be interesting to say the least.
Ferguson's decision to put Darron Gibson on as Ryan Giggs' replacement when the Welshman limped off five minutes before the break suggested there will be no easy way back for Rooney, who celebrates his 25th birthday later this month.
The United manager is far too experienced to require justification for any of his actions. He got it anyway on his side's first real attack.
West Brom might have been aggrieved when Morrison was ruled to have fouled Hernandez on the edge of the area. Much of the punishment was self-inflicted.
Nani's dipping free-kick was difficult to deal with. But Scott Carson should have done far better than merely parry the ball into Hernandez's path.
With no defender accompanying him into the box, the Mexican gleefully tapped home his third goal of the season - two more than Rooney, whose only Premier League effort came against West Ham in August.
The hosts wasted at least three decent chances to double their lead, which meant that Rafael's intervention as Chris Brunt waited to tap home Marc-Antoine Fortune's far-post cross was crucial in keeping their noses in front.
Relief came courtesy of Nani, who capitalised on Nicky Shorey's untimely slip, darted to the edge of the box, then kept going to thrash Dimitar Berbatov's astute return pass into the corner.
Through it all, Rooney remained impassive on the bench, wondering whether he would get a chance to restore his own confidence after an alarming slump which began with the ankle injury he suffered at Bayern Munich in March.
United threatened to score again at regular intervals, although West Brom, winners at Arsenal a fortnight ago, retained an attacking intent that would not pay dividends until after the break.
Given all the attention that had been focussed on the £27million sharpshooter, it was almost forgotten how abysmal United's defending has been at times this season.
Two goal leads had already been thrown away against Everton and Liverpool this season, and Fulham gifted a late equaliser at Craven Cottage.
Yet to see United's advantage wiped out in a six-minute second-half spell was still a shock.
West Brom's first was bizarre and came courtesy of two deflections - off Anderson and Patrice Evra - that took a Brunt free-kick past van der Sar at the near post.
The second was all van der Sar's fault as he inexplicably dropped Brunt's steepling cross to present Tchoyi with a tap-in as unexpected as it was gleefully accepted.
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.
Source: Teamtalk.