Boos rang out after brilliant Bournemouth won 3-0 at Old Trafford for the second season running, with Manchester United's fortunes continuing to yield mixed results under new boss Ruben Amorim.
Erik ten Hag was in charge the last time the Cherries put three goals past Man Utd on home turf a year ago, but a change of manager has not prompted a change of outcome, undone by similar failings and a clear weakness from set-pieces.
The hosts at least worked hard without reward in the first 45 minutes, but shot themselves in the foot after the break and didn't have the guile to respond in the attacking third either, perhaps casting further doubt on Amorim's decision to exclude Marcus Rashford for a third game on the bounce.
Bournemouth teenager Dean Huijsen became the latest player to capitalise on United's lax set-piece defending, glancing home a first-half opener when unmarked from Ryan Christie's free-kick. And that was just the start of a performance that unravelled quite alarmingly.
A quick-fire double in the second period - Justin Kluivert's penalty and Antoine Semenyo's finish two minutes and eight seconds apart - sealed the biggest blow of Amorim's short reign to date, and condemned United to their seventh Premier League loss of the season.
The Portuguese head coach had always warned there would be bumps in the road but a fourth defeat in his ninth match in charge further underlines the severity of issues at hand.
Andoni Iraloa's side leap into fifth in the table, while United are marooned in 13th - the first time they've been in the bottom half of the table at Christmas since 1989-90.
Amorim: We suffer at set-pieces
Man Utd head coach Ruben Amorim:
"It's hard. In this context, it's hard to push for two or three wins. We're trying. But this game was hard on us.
"Without any situation we suffered again at set-pieces. We were a little bit nervous, the stadium.
"We controlled the rest of the first half with some clear chances, and then in the second with the penalty and then another goal is really hard on everyone here.
"In this kind of moment, every thing is hard on us. The set-pieces, the penalty, then we want to score again but we are too nervous. We have to fight this.
"We tried to score but in the end, it was a tough match in a tough situation. We need to move on."
Iraola: We were solid - not amazing
Bournemouth head coach Andoni Iraola:
"I'm happy we were more clinical today, we scored from a set-play, that gives us the chance of having more of a threat because we're a short team otherwise.
"It was a solid performance. Not amazing, but solid. I'm happy we kept playing the same way, kept pushing until the end.
"We have 28 points, that's good, everyone is quite bunched up but to have that at Christmas is a good amount. We have two more chances this week and we'll try to get the maximum there too."