The USA clinched fifth place in the Pacific Nations Cup, which offered a slot at the World Cup, with their 29-13 triumph at the Mile High Stadium.
They had missed out on the last tournament in France in 2023.
Samoa, who have competed at the last nine World Cups and twice been quarter-finalists, will now have to contest a two-legged playoff with Chile to decide one of the two remaining places.
The final spot at the 2027 tournament will be determined by the winner of a four-team playoff tournament in Dubai in November where Belgium and Namibia will compete against either Brazil or Paraguay and the loser of the playoff tie between Chile and Samoa.
The other already qualified nations are Australia (hosts), South Africa (holders), Argentina, Canada, England, Fiji, France, Georgia, Hong Kong, Ireland, Italy, Japan, New Zealand, Portugal, Romania, Scotland, Spain, Tonga, Uruguay, Wales and Zimbabwe.