The Sunderland midfielder, who spent last season on loan at Bologna, was held up by many before the tournament as an example of Italy's inferiority compared to some of their illustrious predecessors.
But he defied his critics by scoring an expertly taken opening goal in a 2-0 win over Group E rivals Belgium at Stade de Lyon, benefitting from a pinpoint Leonardo Bonucci pass.
Italy were then forced to withstand a barrage of Belgium attacks, before Graziano Pelle completed his side's victory after a superb counter-attack in injury time, and Giaccherini was full of praise for his defensive team-mates.
"The defence were definitely fantastic tonight," Giaccherini told a news conference.
"But you don't need me to sit here and say how good Italy's defence is. I think we have the best backline in the competition."
Giaccherini admits he was pleased to silence those who have doubted his suitability to play for the national team, but says his satisfaction was more a consequence of the victory than his own contribution.
"I'm delighted," he added.
"Myself and all of the other players. We all know that whenever we pull on the shirt we are representing the entire nation. It will be that way throughout the competition. Every time you'll see 11 on the pitch and 12 on the bench who are really up for it.
"I'm always willing to help out the team, I always do what the coach asks of me. I'm pleased with my performance but ultimately it's about the team and result above all else."
Giaccherini also rejected suggestions that Belgium failed to show their quality in Lyon after being hailed as one of the pre-tournament favourites.
"Maybe we didn't see it, but we certainly felt it," Giaccherini said.
"Belgium are such a top side on an individual basis. They've got some players who can really hurt you on a one-on-one basis at any stage of the game. Everyone had to help each other out, double up and then when we had the ball we had to try and hurt them, that's what the coach asked us to do."