Coach Branko Ivankovic said Iran paid dearly for poor defending as they lost their World Cup Group D opener to Mexico 3-1 in Nuremburg.
Iran players celebrate their equaliser scored by Yahya Golmohammadi (left)
Rahman Rezaei's dithering on the ball led to Mexico's Omar Bravo scoring an easy second for Mexico and Ivankovic said: "It was a terrible mistake.
"Of course after that it was much harder. We really thought had a chance to do something in this match.
"But we played well in the first half and could have scored more than once."
Ivankovic said, overall, he was satisfied with his team's performance in the first half, which ended 1-1.
"At half-time, I insisted that they start playing more offensively and I was happy with the way they did that."