Marchetti, who was playing in the third division when Italy won the World Cup four years ago, will start against New Zealand in Sunday's second Group F clash after Gianluigi Buffon suffered a back injury during Monday's 1-1 draw with Paraguay.
Marchetti, who spoke to the media for the first time since arriving in South Africa, said his introduction at halftime against Paraguay followed his recovery from a major car crash five years ago.
"After seeing death so close up, something changes inside of you," he told a room full of journalists. "It's hard to explain, it's a bad experience that I carry inside of myself. It will always be a part of who I am."
Marchetti and two friends who were with him in the car during the crash then felt they had "almost a feeling of being persecuted by destiny" when two other friends died in a crash and a third died in another incident.
"I knew before halftime that I would be going on so I had time to mentally prepare," he said. "I'm staying calm and I'm convinced of my own ability. Everything changes from one day to the next but I've always kept the faith."
"Buffon is number one in the world so it's a problem," he told reporters, after training in brilliant sunshine. "But Marchetti has shown at (Serie A side) Cagliari and now in the national team he is a top keeper.
"I saw Gigi (Buffon) yesterday. He feels part of the group and is still smiling. Even if he doesn't play, he is one of us on the field."
