The U.S. trio of Moore, Spencer Levin and Lee Williams finished at 12-under- par 132. Italy was next at eight-under-par 136 while England, Spain and Switzerland shared third place at seven-under-par 137.
Moore, who won this year's U.S. Amateur Championship and U.S. Public Links Championship, played the back side first at the River Course at Rio Mar Country Club and managed three birdies and a bogey over his first nine holes. Moore then caught fire on the front side with five birdies down the stretch for a round of 65.
Williams meanwhile tallied five birdies on the back nine and added a birdie at the first to get to six-under. He then birdied two in a row from the third but found trouble with a double-bogey at the par-five eighth. Williams stumbled again with a bogey at the very next hole for a 67. Levin's 70 was dropped as the team's lowest score.
The Americans are seeking their third straight victory at the World Amateur Team Championship and 13th overall.
Francesco Molinari and Matteo Del Podio carded matching rounds of 68 on the Ocean Course to pace the Italians. Edoardo Molinari was not as fortunate with an opening round of 74.
Sweden and Germany share sixth place at six-under-par 138. El Salvador and the Netherlands followed at four-under-par 140.