The fifth-ranked United States struggled to defend Italian captain Cristian Savani, who had 19 points in the 28-26, 25-20, 25-20 victory for the sixth-ranked Italians.
U.S. setter Donald Suxho bent over with his hands on his knees and shook his head as Italy celebrated the win at Earls Court.
The United States won gold in Beijing, upsetting favourite Brazil 3-1 for their third gold in men's volleyball, which became an Olympic sport in 1964. Russia is the only other nation with three. Italy has won silver twice, most recently in the 2004 Athens games.