Italy manager Marcello Lippi was disappointed his side could only manage a 1-1 draw against Paraguay.
The Azzurri went behind in the first-half after Antonin Alcaraz headed in from a free-kick, but they fought back after the break and equalised as Daniele De Rossi scored prodded home a corner.
New Zealand and Slovakia are the world champions' other two opponents in Group F, and although Italy are still in a strong position to qualify, they would have wanted to kick-off their campaign with three points against the South Americans.
Lippi was happy with the overall performance of his players and believes his side deserved to win.
But he admits there is a sense of regret in the Italy camp and criticised Paraguay for a defensive attitude.
"There is great regret, as this is the kind of match we have got to win," he said.
"There is a great regret, as we certainly deserved to win the game.
"Paraguay scored with their first approach on goal, which can happen from a set play.
"There was a reaction and we played a good game, but this is the kind of match we have got to win, so we need to improve in attack.
"Paraguay preferred to sit back and defend, creating absolutely nothing."
Gianluigi Buffon was forced off at half-time through injury and was replaced by Federico Marchetti.
Lippi has revealed the experienced stopper had a back problem, and does not know if he will recover in time for the next game against New Zealand on Sunday.
He added: "He had a back problem. Will he be fit for the next game? The medical staff have to tell me that."