Italy coach Marcello Lippi has admitted he and his team had underestimated the United States following their 1-1 draw against the 2002 quarter-finalists in Kaiserslautern.
The Azzurri were held by Bruce Arena's battling side in Saturday's bad-tempered game which saw three players sent off - two for the US and one for Italy.
The result means that all four teams in Group E, which also includes Ghana and the Czech Republic, still have a chance of making the last 16.
Italy's draw left them needing a point from their final group game against the Czechs next Thursday to reach the knockout round.
"After our win against Ghana, we thought it was going to be easy against the US but it turned out to be a difficult day," Lippi said on Sunday.
"This is a group of steel and the USA's performance against us proved that.
"On our part there is some bitterness because we had expected a much different performance from ourselves."
Lippi took some consolation from the fact that even a win against the US would not have guaranteed qualification for the last 16.
"If we had won, the situation would not have been much different," said the 58-year-old.
"We would have been faced with less difficulty, but the race for first place would still be a problem.
"Now first place depends all on us, not anybody else."
Lippi admitted the Serie A match-fixing scandal that has engulfed Italian football had affected the players.
"I don't want to make excuses for our performance against the US, but I have seen how hard the boys have worked in these last few months and I've felt the tension," he said.
Lippi sent out a positive message to the Italy supporters, telling them not to give up on the team.
"I would tell all Italians not to lose faith in us," he said.
"We intend to go further in the competition, that's for sure.
"We don't expect to dominate every game - we are not robots. It's not possible. Our fans must understand there are highs and lows, that at times we can make mistakes."
Lippi revealed midfielder Simone Perrotta may miss the Czech game after picking up a hamstring injury.
Italy will qualify for the last 16 as Group E winners if they beat the Czechs. The Italians will also finish top if they draw with the Czechs and Ghana don't beat the USA.