Argentina was comprehensive 3-0 winner at Wembley, as the CONMEBOL/UEFA 'Cup of Champions' was revived for the first time since 1993.
Lautaro Martinez, Angel Di Maria and Paulo Dybala got the goals as Lionel Messi pulled the strings, but in truth Italy were fortunate to only lose 3-0 against a hugely impressive Albiceleste.
It was only Italy's second match since their shock World Cup qualifying defeat to North Macedonia in March, with that loss preventing it from reaching Qatar 2022.
Despite the Azzurri winning Euro 2020 less than a year ago, Mancini is already looking to instigate something of a rebuild.
But he was keen to pay tribute to those who have played a key role over the past four years.
"In the first half we made two mistakes on their two goals, then they were better at keeping the ball," Mancini said.
"They were better than us, but I must say thanks to these guys who have played in these four years.
"There is regret for the lack of qualification for the World Cup, and tonight's match was initially balanced, then they had superior quality to us.
"After this match we had in mind to change several things and we will do it. We need to find the players, put together a team that will suffer at the beginning and that in the future will be able to give us joy."
Clearly, the attack will be Mancini's primary focus in any rebuild as he rued a lack of threat going forward.
"We have great difficulty scoring at the moment, and we have to work a lot knowing that it will not be so simple and it will take time [to overcome their issues]," he continued.
"After the European Championship we struggled to score and we have to find solutions in this sense and try to be fast, but it will not be easy to put together a team that gives us short-term satisfaction even if there are good guys. We will have to make as few mistakes as possible.
"I have optimism. I like to work and train. It's true that we lost against a great Argentina team, but we must know that there will also be these moments and we must make sure that the youngest players learn quickly."
Italy now turns its attention to the Nations League. It faces Germany on Sunday and again on 15 June – matches against Hungary and England are sandwiched in between.