The uncomfortable truth David Moyes faces after this reverse is that here was a display as concerning as last Sunday's derby humiliation at Manchester City. West Bromwich Albion cruised through this in a manner that the champions of England should not countenance on their own turf. A repeat of the 4-1 scoreline at the Etihad Stadium could have happened to a United side who missed key performers and whose display prompts questions regarding Moyes's selection.
The starting XI featured the less-heralded Alexander Büttner, Anderson, Shinji Kagawa, and Javier Hernández, the latter in for a Robin van Persie, who was on the bench following a groin injury before making an unconvincing 30-minute cameo.
Kagawa, playing on the left, was taken off at the break for the 18-year-old Adnan Januzaj, with Moyes confirming this was a tactical substitution. "I just decided that I wanted to try and make a change, try and inject a little bit of something and I thought Adnan showed what he could do," he said. "We want Shinji to feel he's getting an opportunity to show what he can do. His best position may be No10 but even for Japan he plays off the left as well so it's not something which is strange to him or not his position so he's used to that. But there's a lot of competition here and we want to push each other on to give performances and improve."
The Scot's team just could not live with a Baggies side who zipped the ball around and gave United a footballing lesson, a sight not often seen in this parish. Now, the champions stare at a Premier League table that shows them in 12th, their seven points leaving them only three above the drop zone, after six games.
Steve Clarke's men were not as stellar as City had been but, though United rallied towards the end, the sense was of a home display almost as insipid as the one they turned in during that 166th edition of the local squabble.
This had the joyous travelling support singing, "We'll sack who we want, we are the Albion, we'll sack who we want," as they took over United's backyard for the afternoon.
The contest featured the two finest goals seen here so far this season. As Clarke would comment, one was a supreme individual effort, the other a collective offering also converted by a superb finish.
Both were scored by West Brom. First, Morgan Amalfitano took possession and proceeded to skate at Rio Ferdinand, nutmegging the veteran defender before dancing towards David de Gea and dinking a sublime chip over the keeper.
This was on 54 minutes. Within seconds United were level. Perhaps being unhappy suits Wayne Rooney because the forward, who has started the campaign like a juggernaut, collected a fifth goal in six games when his free-kick came bending from the left and missed everyone, including the visiting keeper, Boaz Myhill, and that was 1-1.
This was not the end of the West Brom challenge, though. Amalfitano nearly added a second with a zinger of a free-kick that De Gea tipped over superbly. Then, the Frenchman contributed to Saido Berahino's strike with a pivotal touch from Stéphane Sessègnon's pass, the ball falling into the Burundi man's path for him to let fly with a bullet that gave De Gea no chance.
"They were two great goals," Clarke said. "The first was individual but the second was a good team effort, we played the ball neatly around the area.
"Saido does what he does best, he scores goals. It is good for everyone, especially for him as he has worked hard to get where he is. He is giving me lots of headaches as he is pushing himself into the team."
Moyes added: "We did not defend well at all but we didn't attack well either today. We had a lot of the ball in the first half but didn't make the most of it. We had one or two chances but just didn't take them."
A smattering of boos could be heard as the close. "No worries about the crowd because it was great," the manager said. "The stadium in midweek was in great voice. People come here expecting us to play well but we didn't play well. We tried to pick it up in the second half but we got done by it as well. You're always going to have bad results. It is how you deal with them. There are lots of games to come and it's about how you deal with them, so we look forward to them."
United did overcome Liverpool in the Capital One Cup on Wednesday but, before what had been a first chance to return a league win since the reverse to City, Moyes described the mood at the club as "embarrassed" following that performance.
He may feel the same now.