Arsene Wenger believes a failure to "be rigorous until the end" cost his team at Swansea City on Sunday.
Alexis Sanchez opened the scoring for the Gunners in the 64th minute, but conceded two goals in three minutes to slip to a second defeat of the season.
Wenger was particularly dismayed to lose after what he felt was, for long periods, a disciplined performance.
"When you’re 1-0 up in a game of that importance, it’s very, very disappointing"
"It’s disappointing because we were in control of the game and we missed some decisive challenges in the middle of the park and that is not acceptable," he told Arsenal Player. "When you’re 1-0 up in a game of that importance, it’s very, very disappointing.
"The game changed with the free kick - before the free kick we had the ball and we are guilty of what happened there. We were completely in control and it was just a question of not making mistakes and being serious so that we could score the second goal.
"We have to take the consequences of that defeat. I didn’t expect that from my players but I felt what happened after Tuesday night that we would be rigorous until the end - unfortunately we weren’t.
"Football lives from having everything right. Sometimes when a few things are not right you can pay for it and that’s what happened."
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