Finau Maka crossed over for Tonga in the first two minutes
USA: (3) 15
Tries: MacDonald, Stanfill
Tonga: (13) 25
Tries: Maka, Vaka, Vaki
Cons: Hola 2
Pens: Hola 2
Tonga got their World Cup campaign off to a winning start with victory over a battling USA in Montpellier.
The Americans found themselves 13-0 down after 26 minutes thanks to an early try from Toulouse flanker Finau Maka and two Pierre Hola penalties.
Eagles prop Mike MacDonald made the score 13-8 with a try in the corner but Tonga responded through Joseph Vaka.
USA flanker Louis Stanfill then crossed from close range but Viliami Vaki's superb score sealed victory for Tonga.
The result was a disappointing one from America's point of view following on from their impressive display against England last weekend.
They seemed to be feeling the effects of the quick turnaround and Tonga made an explosive start with Toulouse's Maka going over after a rolling maul from a line-out after 72 seconds.
America settled however and restricted the combative Tongans to just two Hola penalties in the rest of the opening half.
The Eagles, boosted by a Hercus penalty just before the break, dominated for long periods of the second period and twice got back to within a score of their opponents.
MacDonald powered his way over to score in the corner on 46 minutes but Tonga responded with the help of an incisive break from skipper Nili Latu which led to Joseph Vaka scoring his first try for his country.
America had renewed hope when Stanfill bundled over from his own tap penalty but Vaki struck the decisive blow with 10 minutes left - leaving the Eagles ruing their wasted opportunities.
USA try-scorer Louis Stanfill:
"People might think our performance against England had an effect, but we won't be using that excuse.
"That's an easy excuse to use."
Tonga captain Nili Latu:
"I told the boys to be patient. I also told them again what our game plan was because we weren't sticking to it at that point.
"I'm very pleased. It's not often you get the chance to play in a World Cup and it's a good feeling to get a victory. Winning today is a confident step up for us."
USA: Wyles; Sika, Tuipulotu, Esikia, Ngwenya; Hercus (capt), Erskine; Bloomfield, Clever, Stanfill, Mangan, Alec Parker, Osentowski, Lentz, MacDonald.
Replacements: Burdette, Moeakiola, Mexted, Basauri, Petri, Malifa, Eloff.
Tonga: Lilo; Tu'ifua, Hufanga, Taione, Vaka; Hola, Havea; Maka, Latu (capt), Pole, Hehea, Fa'aoso, Pulu, Lutui, Tonga'uiha.
Replacements: Taukafa, Toke, Vaki, Filipine, Tu'ipulotu, Tupou, Havili.