Iran manager Branko Ivankovic conceded his team were beaten by a moment of genius from Deco in their 2-0 Group D defeat to Portugal in Frankfurt.
The Barcelona playmaker broke the deadlock on the 62nd minute with a 25-yard strike before Cristiano Ronaldo doubled the score in the 78th minute.
"It was hard to make something happen on the field against a good Portugal team," said Croatian Ivankovic.
"Deco scored a quality goal. After that it was very hard for us to equalise."
The defeat means Iran cannot qualify for the last 16 after losing 3-1 to Mexico in their opening Group D game.
And striker Vahid Hashemian admitted Iran's disappointing performance was the responsibility of the players.
"Forty-five minutes are not enough, you have to run for 90 minutes," he said.
"We were the better team against Mexico but today we deserved to lose."
Despite the end of their qualification hopes, Ivankovic insisted Iran will take their final game against Angola seriously.
Iran will be trying to earn their second win in the finals following their defeat of the USA in 1998 and he said: "I want my players to treat it like life and death.
"We should not need motivating just because we are out."