Samoa (22) 25
Samoa survived a late USA rally to win in St Etienne
Tries: Fa'atau, A Tuilagi, Thompson
Cons: Crichton (2)
Pens: Crichton (2)
USA (3) 21
Tries: Ngwenya, Stanfill
Pens: Hercus (3)
Samoa ground out a stuttering 25-21 victory against the USA in their final Pool A match in St Etienne.
The Samoans went ahead through right wing Lome Fa'atau after five minutes and doubled their tally soon after when left wing Alesana Tuilagi dived over.
The Eagles managed to stem the tide until just before the break when Samoa's Kane Thompson scored a third.
USA hit back with a try from wing Takudzwa Ngwenya but they fell short despite Louis Stanfill's late score.
Samoa lost heavily to South Africa in their first game before losing to Pacific Island rivals Tonga and then England to end their hopes of progressing to the knock-out stages.
USA still have to play pool leaders South Africa on 30 September in Montpellier but are likely to go home without a win in their four group matches.
We've spent more time in valleys than on the mountain tops
Samoa coach Micahel Jones
Samoa were brisk and bristling from the start and quickly pounced on a free ball under the USA posts, with London Irish centre Seilala Mapusua passing to Fa'atau to slice over.
Soon after, fly-half Eliota Fuimaono-Sapolu made the first of several useful breaks, and fed giant winger Alesana Tuilagi, who crashed over in the left corner on nine minutes.
Loki Crichton kicked the conversion, but the USA clawed some points back when Mike Hercus slotted a penalty.
Shortly before the break, Samoa went over again when Fuimaono-Sapolu slipped one tackle and offloaded to Elvis Seveali'i who popped a ball back inside for Thompson to scamper over.
It looked like business as usual at the start of the second period as Samoa dominated but Fa'atau and Seveali'i both squandered clear-cut chances to score as they spilled the ball in acres of space.
USA nearly made Samoa pay when Eagles full-back Chris Wyles, chasing a kick ahead, almost beat the casual Crichton to the touch down.
Eagles' number eight Fifita Mounga gave his side even more of a mountain to climb when he was sin-binned for deliberately slowing down ruck ball on 50 minutes.
But almost immediately, the USA launched their renaissance when Harare-born flyer Ngwenya danced past two Samoans to score in the right corner for 22-10.
We toughed it out and the US public like to see that - they like to see effort put in
The Eagles enjoyed a real purple patch and Hercus' second penalty gave USA a real target to chase.
Crichton's 70th-minute three-pointer looked to have ended the contest but Hercus' third kick gave hope to the Eagles, boosted by the sin-binning of Samoan replacement Silao Vaisola Sefo for a late challenge.
The Eagles pushed hard inside the last five minutes and went close again through Ngwenya before blind-side Stanfill muscled over at the death.
Mounga was carried off on a stretcher after a heavy tackle in the second half and was immediately taken to hospital, but coach Peter Thorburn played down the extent of the injury.
"He's got feeling in both hands and in his neck," he said. "They are taking him away for an MRI scan but it looks pretty positive."
Outgoing Samoa coach Michael Jones:
"It is wonderful to get a win. We have been waiting for this, and it is important that we achieved it.
"I am a strong believer in the potential of Samoa. And in the first 40 minutes, I'm pretty sure the rugby world saw what we were capable of.
"We didn't do too well in periods of the second half, like in the last 10 minutes against England and when we lost to Tonga.
"It's been that kind of journey for us - we've spent more time in valleys than in the mountain tops.
"We have under-achieved. The expectation of our people was for us to do better and I take that on my shoulders as coach.
"We need to take time to analyse why we didn't fulfil the potential. We showed glimpses but weren't capable of doing it when it mattered, for 80 minutes."
USA captain Mike Hercus:
"I think at the end we played really good.
"We've really got in the habit of being slow starters. The spirit of rugby was there. Hopefully we entertained people."
USA coach Peter Thorburn:
"It's a mystery why we fell away early on.
"We didn't get the set-piece right or any line-out ball. Nothing magic was said at half-time but we improved.
"I think they got a little too far ahead at 22-3, but we toughed it out and the US public like to see that. They like to see effort put in."
Samoa: Loki Crichton, Lome Fa'atau, Seilala Mapusua, Elvis Seveali'i, Alesana Tuilagi, Eliota Fuimaono-Sapolu, Junior Polu; Kas Lealamanua, Mahonri Schwalger, Census Johnston, Leo Lafaiali'i, Kane Thompson, Semo Sititi (c), Justin Purdie, Alfie Vaeluaga.
Replacements: Silao Vaisola Sefo, Naama Leleimalefaga, Joe Tekori, Ulia Ulia, Steve So'oialo, David Lemi, Lolo Lui.
USA: Chris Wyles, Salesi Sika, Philip Eloff, Vahafolau Esikia, Takudzwa Ngwenya, Mike Hercus (c), Chad Erskine; Mike MacDonald, Owen Lentz, Chris Osentowski, Alec Parker, Hayden Mexted, Louis Stanfill, Todd Clever, Fifita Mounga.
Replacements: Blake Burdette, Matekitonga Moeakiola, Mark Aylor, Henry Bloomfield, Mike Petri, Valenese Malifa, Albert Tuipulotu.