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.
As a sign of thanks for his survival he had the Hail Mary inscribed as a tattoo and said he would grab his chance while he could to shine for his country.
The 27-year-old, who had little to do against Paraguay in his sixth cap, is also likely to start when Italy play Slovakia in their final group game on June 24 as 2006 winner Buffon takes time to recover from a small herniated disc.
"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."
Marchetti, who moved into goal after playing as a striker in his youth, said the 32-year-old Buffon had already provided support and advice and told him to just relax in goal.
However the younger keeper, who described himself as more explosive than Buffon, said he thought the pressure had increased on goalkeepers who cannot afford to make one mistake at this World Cup given the lighter ball.
Italy left back Domenico Criscito gave Marchetti an endorsement, of sorts.
"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."
