The Gunners saw their 100 per cent record at home in the Premier League ended by a ruthless counter-attacking display from United, who raced into a 2-0 lead inside 11 minutes and withstood a barrage of pressure to see out the win.
The result left Arsenal 15 points behind leaders Manchester City, their hopes of a first league title since 2004 looking decidedly slim.
Wenger says he spoke with the players immediately after the loss to Jose Mourinho's side, having been frustrated to see them create so many chances but fail to earn a result.
"Everybody has a little bit his own analysis. But my opinion counts," he said.
"You know you have a very clear-the-air [talk] straight away when you have a defeat like that, a disappointment like that. You try to analyse it straight away with the players to get it out of the system and focus on what is in front of you.
27 - Arsenal have had the same tally of shots on target in their last two competitive matches (27: 16 vs Man Utd and 11 vs BATE) as Swansea City have had all season in the Premier League (27 in 15 games). Playground. — OptaJoe (@OptaJoe) December 7, 2017
"I felt that it took our players time to get into the game. It took them a while to adjust to the pace of the game and they had the power up front and they surprised us a little bit with their pace and after that we played remarkably going forward but, as well, we did not take enough of our chances. We were not clinical enough.
"I am looking just at the numbers and we had a very strong creative performance, with a high, high, high amount of expected goals. And we had a poor defensive performance."
Wenger started the match with a back three but shifted to a four-man defence after United scored their second through Jesse Lingard, with Alex Iwobi replacing the injured Shkodran Mustafi to boost their chances of a comeback.
The Gunners boss has conceded he would prefer to play with a back four on a more regular basis but will always adjust depending on the circumstances.
"I decided to play with a back four," he said. "It is my preferred system. But I adjust always what suits the players, the quality of the players, the balance of the team.
"I went to a back four as well as we were 2-0 down and I put on an offensive player as we had to come back. But it can change."