Arsenal boss Arsene Wenger described Swansea City as a team "who refused to play" after seeing his side's unbeaten run come to an end.
Bafetimbi Gomis caused a major shock at the Emirates after scoring with a header in the 85th minute with Arsenal failing to restore parity in the dying minutes of the game.
And the Frenchman blamed a lack of patience for his side's defeat.
"We were unlucky I think against a team who refused to play completely and just defended," Wenger said.
"I cannot say that they played a lot. I don't know how many passes they made tonight, I haven't seen the stats. They came here to defend and they didn't play. We couldn't take advantage of it.
"It was a question of being patient enough and if we couldn't win it not to lose it. Overall I was encouraged by the quality that we showed in the second half, but it's frustrating.
"When you cannot win a game, don't lose it. We knew exactly what could happen. It was not even a break. We were warned of the kind of goal they could score with Montero kicking the ball in the air and we were short in jumping for the ball.
"For the rest we rushed our finishing because we had plenty of chances in the second half. It was just a question of scoring a goal.
"We still have a game in hand. What is crucial is to respond on Sunday and show that it was an accident today. That is the most important thing."