As a trio of dominant Korean archers crumbled under pressure during the day and fell out of contention before the semi-finals, Galiazzo sensed his chance to snatch a surprise win.
"This morning I kept telling myself no one is unbeatable. Then when I saw all the Korean archers had been beaten I knew I had a great chance," the 21-year-old Italian said.
In the 12-arrow shootout at the marble home of the modern Games in Athens, the Panathinaiko Stadium, Galiazzo fired five bullseyes for maximum 10-point scores to take the final 111-109.
He was just a year old when Yamamoto last stood an Olympic podium: "It took me 20 years from winning bronze at the 1984 Olympic Games in Los Angeles to win silver here today," Yamamoto smiled. "Now I have to wait 20 more years to win the gold."
"I didn't expect to win this medal," Galiazzo said. "It's an incredible experience to know that everything you have worked for over the last four years can come together in one day.
"I think it will take at least four days for me to come to terms with this."
Seventeen-year-old Australian school student Tim Cuddihy won the bronze after upsetting two Koreans before the semi-finals to create an open race for the title.
Cuddihy, who lost to Yamamoto in a semi-final tiebreak after both archers equalled the Olympic 12-arrow record of 115, held his nerve to beat Briton Laurence Godfrey 113-112 for bronze.
KOREANS FALTER
Unlike the South Korean women who have won every gold medal up for grabs since first competing at the Games in 1984, the country's record breaking men have failed to live up to their team reputation in the individual competition at Olympics.
Again they faltered in the big matches.
They started the day well, with Park Kyung-mo setting a new Olympic 18-arrow record in the round of 16, to go with Im Dong-hyun's 72-arrow world best in the ranking round. Koreans also hold the world 18-arrow and 12-arrow records.
But by the semis they were out and the black spot on a brilliant Olympic record -- no individual title -- remained.
In a country where soccer is national obsession, Galiazzo took up a sport which may be steeped in centuries of tradition, but was unfamiliar to his friends. When they went to play soccer, he picked up his bow and shot arrows.
"I honestly never had a problem with that. They went to play football and I went to practise my archery," said the quietly spoken student from the northern city of Padua.
But Galiazzo, ranked second in Italy behind world champion Michele Frangilli, said childhood friends did not tease him:
"If anything, when I started winning for my country my friends began to envy me, and started to realise what the sport was about and started to support me."