"We lacked punch in the first half; we did more in the second half, which gave us the lead, but unfortunately, we probably relaxed a little too much.
"We mustn't concede that second goal. They didn't have any chances; they had two shots on target, that's two goals.
"They did the opposite against Ukraine (a 5-3 defeat on Friday, editor's note) with six (seven) shots on target and five goals conceded. We made a mistake defensively with that second goal," Deschamps said in his post-match press conference.
"That shouldn't happen to us. Maybe we were still celebrating our second goal. We were high up the pitch, and we were badly positioned," added the coach after the match.
Deschamps also complained about the refereeing, saying the Icelanders' opener was invalid.
"The first goal isn't valid. I've seen it several times, and it was a foul (by Victor Palsson on Manu Kone, editor's note).
"I'm not going to sum up the match on that, but with zero chances, they were 1-0 up at half-time. But I'm not taking anything away from this Icelandic team, who showed they had quality," he said.
Deschamps also praised the performances of France's two goal scorers, Christopher Nkunku and Jean-Philippe Mateta, who kept up appearances in the absence of their key forwards, all of whom were injured. They were without Kylian Mbappe, Ousmane Dembele, Marcus Thuram, Bradley Barcola, and Desire Doue.
Nkunku "had a first half where he was more in charge. He has the ability to get inside and hit the ball.
"He's not in top form, he's had less playing time at Milan, he was injured before, but he's very skilful in front of goal," Deschamps said about Nkunku.
As for Mateta, who celebrated his first start for the Blues at the age of 28 with his first goal, Deschamps noted that the game had "not been easy for him in central midfield with big players."
"He didn't get many balls in the first half. I would have liked to see more crosses because he's an effective player in the box, but to be able to score that goal is a very good thing for him," he also said of the Crystal Palace striker.
