Ole Gunnar Solskjaer admitted Manchester United "never turned up" as Arsenal inflicted another home defeat in the Premier League on the Red Devils with a 1-0 win at Old Trafford on Sunday.
Pierre-Emerick Aubameyang's penalty earned the Gunners first away win against 'big six' opposition in 30 attempts in the English top flight.
In Solskjaer's 100th game in charge, United were brought back down to earth with a bang after thrashing RB Leipzig 5-0 in the Champions League on Wednesday.
A sixth straight league game without a win at home leaves United down in 15th.
"We never turned up in the first half, they were better than us," said Solskjaer. "We weren't at the races."
Solskjaer stuck with the 4-4-2 system that demolished last season's Champions League semi-finalists Leipzig in such stunning fashion as he tried to accomodate Paul Pogba and Bruno Fernandes in the same midfield.
But that backfired as Pogba's naive challenge on Hector Bellerin gave away the decisive penalty and United looked short of ideas on how to break down Arsenal's well-drilled defence.
"Stay on your feet. Paul knows he's made a mistake there," added Solskjaer, who hinted complacency may have been to blame for his side's display.
"When you've played well, sometimes you take your foot off the pedal. That's not how it works."
However, Solskjaer played down the significance of United's home form, with his side simultaneously on a club-record run of 10 straight away wins in all competitions.
"Home and away form is out the window with no fans in the stadium, 100 percent.
"Just look at the stats now with the amount of away wins all over. Home form away form doesn't mean too much."
- Arsenal going places -
By contrast, Arteta was delighted by his side's discipline as they bounced back from losing three of their last four league games to move back within a point of the top four.
"I didn't want to tell the players we hadn't won here in 14 years," said the Spaniard. "But the team you saw tonight is what we are starting to be. I am proud with the personality we showed to play at Old Trafford and delighted with the win."
The day started in sombre fashion for United as they remembered former great Nobby Stiles, who died at 78 this week, and confirmed the news that another legend of the club Bobby Charlton is suffering from dementia.
On the field, there was precious little to lift the mood as Arsenal's press prevented United from getting into any sort of rhythm.
All that was missing from Arteta's men was again a greater cutting edge going forward as they have now gone three league games without scoring from open play.
Willian struck the bar for the visitors after a well-worked one-two with Aubameyang before Bukayo Saka headed the best chance of the half over the bar.
Arsenal continued to pose the greater threat after the break as Aubameyang curled wide the sort of half-chance he has made his speciality from the edge of the box before the outstanding Thomas Partey stung the palms of David de Gea.
After a starring role against Leipzig, Solskjaer recalled Pogba to the starting line-up in the Premier League for the first time since a 6-1 thrashing by Spurs a month ago.
But a moment of ill discipline from the Frenchman finally gave Arsenal the breakthrough 21 minutes from time as he needlessly dived in to clip Bellerin inside the box.
Aubameyang had not scored in the league since ending speculation over his future by signing a new three-year deal six weeks ago, but kept his cool to break his scoring drought by sending De Gea the wrong way and score Arsenal's first goal in the Premier League for 277 minutes.
"It's a very big win," said Aubameyang. "We knew since the beginning we have to trust the process, Mikel is bringing something very nice."
The visitors then held out doggedly with the closest United coming to an equaliser when Mohamed Elneny and Leno combined to turn Donny van de Beek's cross onto their own post.