Ole Gunnar Solskjaer accused his Manchester United players of treating their game at Watford as a testimonial after they slipped to a shock defeat against the Premier League's bottom side.
A David De Gea howler allowed Ismaila Sarr to open the scoring before Troy Deeney's penalty four minutes later secured a 2-0 victory and a first home win of the season for the Hornets.
United were poor for much of the contest but improved slightly following the introduction of Paul Pogba, who came off the bench to make his first appearance since September following an ankle injury.
The Red Devils have struggled against teams in the bottom half of the table this season and have won just one of the last 17 games in which they have enjoyed a larger portion of possession.
Solskjaer's side will sit eighth in the table on Christmas Day as hopes of a top-four finish continue to dwindle, and the Norwegian pulled no punches in assessing United's performance at Vicarage Road.
"The first half it could easily have been my testimonial," he said.
"And it might have been a better atmosphere at my testimonial, to be fair. It was very subdued, slow, no tempo, urgency.
"Any bit of encouragement their crowd got was when we gave them set-plays. And we gave them two goals in the second half.
"Today is not about the amount of possession - it's about quality, how we do things and the two goals we conceded.
"The first one, a big goal, was from a mistake. The second goal as well, it's a bad mistake making a tackle. So two goals in three minutes made it hard for us."
Recent victories over Tottenham and Manchester City had suggested United had started to turn a corner under Solskjaer.
But a home draw to Everton was followed by this dismal display in Hertfordshire after the team coach arrived less than an hour before kick-off.
"I'm very disappointed," Solskjaer added.
"We have started off something with the rebuild but today I am very disappointed because you have to come to these stadiums and get more points against teams like today.
"I am sure they were low in confidence because they are at the bottom of the table. We are high in confidence but it just wasn't there. There was no intent or urgency to make us win the game.
"We prepared well. There is nothing I can put my finger on. You can't blame the traffic. We were a little bit late but an hour here should be enough to prepare."
Harry Maguire captained United and echoed his manager's sentiments that they have to learn how to improve results against the lesser sides in the Premier League.
"We were sloppy, we gave the ball away numerous times especially in the first half," he told Sky Sports.
"We have got to be better against these lower opposition who have a deep block. The first goal is crucial.
"We didn't keep the ball in their half for long enough. Every time we kept it we gave it away and they ended up counter-attacking."
For Watford, this could prove to be a marquee moment in their fight against the drop.
Nigel Pearson inspired a maiden home win of the campaign in his first game in the Vicarage Road dugout.
He felt his side performed better last time out in defeat a league leaders Liverpool, but was encouraged by what he saw on Sunday.
"It was important after Liverpool that we tried to emulate the positive aspects of that performance," the former Leicester boss said.
"We have talked a lot this week about having a positive intent. When you play the stellar teams in the Premier League it is important to function well as a team and we did that. We were organised, we were disciplined.
"I did not think we played quite as well as we did last week. To be sitting here on December 22, and that's our first home win, it's incredible really.
"It was going to be important today to get the performance right. It is a big day to be able to see or experience the reward for working hard.
"In the context of our season it was a very important result to stay in contact with teams. It is not something we should go overboard with."