Tonga recovered from defeat against Italy last weekend to defeat USA 22-13 at Parc Eirias in Wales.
Winger Fetu'u Vainakolo grabbed the opening score for the Islanders with a try after ten minutes, before the USA's Luke Hume looked to have levelled the scores only for this try to be ruled out for a forward pass.
USA fly-half Zachary Pangelinan then added a penalty after half an hour to put the Eagles on the board, before scrum-half Robbie Shaw put them ahead with a try right on the stroke of half-time to leave the score at 5-10.
Tonga were down to 14 men at the start of the second half after fly-half Fangutapu 'Apikotoa was penalised for a deliberate knock on, Pangelinan stretching the lead to 5-13.
Full-back Vungakoto Lilo responded with a penalty for Tonga to close the gap before a try from Joe Tu'ineau sent the Islanders ahead with only 15 minutes remaining.
Perpignan centre Sione Piukala then added another try for Tonga to put the match out of sight.
Tries: Vainakolo, Lilo, Piukala
Cons: Lilo 2
Pens: Pangelinan 2
Tonga: 15 Vungakoto Lilo, 14 Fetu'u Vainakolo , 13 Sukanaivalu Hufanga, 12 Sione Piukala, 11 Viliami Helu, 10 Fangatapu Apikotoa, 9 Taniela Moa, 8 Viliami Ma'afu, 7 Nili Latu (capt), 6 Steve Mafi, 5 Lua Lokotui, 4 Joseph Tuineau, 3 Halani Aulika, 2 Elvis Taione, 1 Alisona Taumalolo.
Replacements: 16 Ilaisia Ma'asi, 17 Kisi Pulu, 18 Tevita Mailau, 19 Hale T Pole, 20 Joshua Afu, 21 Viliame Iongi, 22 Edmond Paea, 23 Alipate Fatafehi.
USA: 15 Zachary Pangelinan, 14 Cornelius Dirksen, 13 Paul Emerick, 12 Andrew Suniula, 11 Luke Hume, 10 Toby L'Estrange, 9 Robbie Shaw, 8 Todd Clever (capt), 7 John Quill, 6 Scott LaValla, 5 Louis Stanfill, 4 Brian Doyle, 3 Eric Fry, 2 Chris Biller, 1 Shawn Pittman.
Replacements: 16 Derek Asbun, 17 Nick Wallace, 18 Zachary Fenoglio, 19 Inaki Basauri, 20 Peter Dahl, 21 Mike Petri, 22 Rolan Suniula, 23 Gearoid McDonald.