Man Utd boss Ole Gunnar Solskjaer admitted his side may have taken their foot off the pedal versus due to their commanding victory over RB Leipzig in midweek.
The Red Devils were second best throughout in their 1-0 defeat against Arsenal.
The game’s defining moment came midway through the second half when Paul Pogba conceded a penalty that Pierre-Emerick Aubameyang duly dispatched.
Speaking to Sky Sports after the match, Solskjaer said: “When you have played well you think you can take your foot off the pedal but that is not how it works because this was a big game against a good team and you have to be absolutely spot on with everything.
“If you are slightly late for a tackle they get away from you and you give a foul away and we weren’t at the races.
“We were too sloppy, too many passes went astray and the rotation was not there.
“Too many things that can go wrong in a game did for us today. Today we didn’t get the response we hopes for.”
Regarding the penalty incident, Solskjaer said of Pogba: “He needs to stay on his feet. Paul [Pogba] knows it’s a soft penalty to give away similar to Nemanja [Matic] who almost got a penalty.”
The home defeat extends their poor league form at Old Trafford this season, but the Norwegian insisted home and away form is largely irrelevant without fans in attendance.
“Home and away form is out the window with no fans in the stadium,” he added. “You can’t look at that. It doesn’t really mean too much. We played fantastic on Wednesday and now we lose. But we need to get points on the board. Now we need to focus on next week and Everton.”
When quizzed on how he and Man Utd will react, Solskjaer said: “I’ll just keep on working. It is a good group that wants to win, go forward and work hard. Today they will go home disappointed but I know these boys and they will get back at it.”
Maguire bemused by loss
Man Utd captain Harry Maguire insisted he and his teammates won’t offer excuses for the defeat, but surprisingly revealed he was at a loss to identify the reasons why they lost.
“It’s hard to put your finger on it,” said the centre-half. “It was disappointing from us. It was a cagey game, a game of few chances.
“We needed to do more, we needed to create more.
“We were confident going into the game. It was important to start the game well. We just gave the ball away too much.
“It’s not good enough, we’ve got to go work hard tomorrow at training.
“We can’t find excuses, we’ve got to look within.
“We haven’t won in the league at Old Trafford this season. It’s disappointing, we want teams to have a tough time coming here.”