Italy coach Marcello Lippi was left seething by his side's performance in the 1-1 draw with the United States.
"I'm disappointed and angry," said Lippi, after 10-man Italy failed to beat the US, who had two men sent off.
"We didn't go into this match in the right frame of mind and we paid for that with the nervous way we played and with the mistakes we made."
Lippi said of the red-carded Daniele De Rossi: "I'm sorry as he's a good kid but he's made the umpteenth mistake."
The Roma midfielder was dismissed for elbowing Brian McBride in the face in the 28th minute, shortly after the USA had equalised.
"I'm sorry for myself, my team and the fans," said the 22-year-old.
"I didn't intend to harm him. I talked with him and now I'm hoping the punishment isn't too harsh. I feel terrible about it. I explained what happened with McBride and he was very kind."
Lippi added: "We didn't play our best game. It was simply not our night.
"My players got nervous and they made very serious mistakes, like that of De Rossi.
"That was a very serious error and we paid the consequences."
Lippi admitted the Americans were the stronger team, despite their two red cards.
"They were very organised, went out really motivated, determined to get a result," he said.
"They showed a lot of quality and heart and this result leaves everything up in the air.
"But it's not a negative result. I am happy that today our World Cup starts because this is a wake-up call for us. From now on is simply a case of being in or out."
Italian midfielder Gennaro Gattuso added: "We weren't brilliant."
Italy had won their opening Group E game in style when they beat Ghana 2-0, but Lippi's side were unable to repeat that level of control against the US.
"It just goes to show how you've got to keep your feet on the ground, even after winning your first match," said Gattuso, who came on as a substitute for Francesco Totti after De Rossi's first-half dismissal.