They collected tries through captain Sergio Parisse (after only a couple of minutes), first five-eighths Luciano Orquera and prop Martin Castrogiovanni in the first half.
The USA, in their last hurrah at this tournament, scored an excellent try through fullback Chris Wyles, who followed up a powerful tackle-busting break by centre Paul Emerick.
The Eagles will depart safe in the knowledge that they got the one victory they were after - against Russia.
Ireland and Australia should progress to the quarter-finals, but Italy could still have a say in which way the big two go. Australia, three points behind Ireland, play Russia on Saturday and will expect five match points. They would dearly love the Italians to upset Ireland and provide them with an 'easier' route to the final against Northern Hemisphere opposition.
In a sometimes feisty clash, Todd Clever - all perspiration and ponytail - was a powerful force at flanker for the Americans, while centre Emerick impressed with his straight running.
Italy flanker Parisse was direct with the ball and Castrogiovanni a rock at tighthead prop.
Italy 27 (Sergio Parisse, Luciano Orquera, Martin Castrogiovanni, penalty try, tries; Mirco Bergamasco 2 cons, pen).
USA 10 (Chris Wyles try, con, pen).
HT: 20-10.
ITALY 27
USA 10