Man of the match Tim Nanai-Williams and captain Ofisa Treviranus scored the tries while the boot of Tusi Pisi and Mike Stanley ensured the Manu maintained their lead throughout the match.
The US continued to question the Samoan defence, with the power of Thretton Palamo and raw pace of Takudzwa Ngwenya a constant threat, and managed a consolation try in the final minutes.
Coach Stephen Betham says there is plenty to work on but they're happy to take the win and move on.
