Fiji moved into a Pacific Nations Cup final matchup against either Japan or Samoa after beating the United States 22-3 in Tokyo on Saturday.
Fiji, the defending champions, were made to work hard in the semi-final against an American side that finished as runners-up in their group in a revamped tournament format.
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But the Fijians, who beat both Samoa and Tonga to top their first-round group, made their class tell and preserved their record of not conceding a single second-half point in the competition.
Japan and Samoa face off in Sunday's second semi-final in Tokyo for the right to play Fiji in next weekend's final in Osaka.
"USA came out today wanting to go to the final too," said Fiji captain Tevita Ikanivere, who was sin-binned in the second half.
"It wasn't good me getting the yellow card, not leading by example. But I thank the boys for turning out and finishing the job today."
Fiji made a slow start and found themselves three points down midway through the first half after a penalty from the USA's Chris Mattina.
Caleb Muntz levelled the score with a penalty of his own before Fiji bagged the first try of the evening when Elia Canakaivata rumbled over in the 26th minute.
Canakaivata doubled his tally in the 51st minute, finishing off a move down the right wing.
Fiji's task was complicated when Ikanivere was sin-binned in the 55th minute, but Frank Lomani stretched their lead with a third try just before the hour mark.
"We wanted to meet their physicality, I think that was a big part of our game," said USA captain Nate Augspurger.
"It did feel sometimes that we were able to put dominant shots in, force knock-ons and getting them on their backs, it's just that second half got away from us."
Tonga beat Canada 30-17 in the fifth-place play-off earlier in the day.
Winger John Tapueluelu scored a double as the Tongans held off a gutsy effort from the Canadians.
Canada kept themselves in the fight until the end before Tapueluelu's second late in the game sealed the win for Tonga.
