Wales became the first side to be eliminated from the Rugby League World Cup as the United States secured a deserved win at the Racecourse.
Christiaan Roets scored the opening try but the Tomahawks responded through Clint Newton and Matthew Petersen.
Man-of-the-match Joseph Paulo, Newton and Tuisegasega Samoa added further tries for the United States.
Wales rallied with late consolation tries from Roets and Anthony Walker but the result had long been decided.
The game was a must-win for Iestyn Harris's side after defeat by Italy in their opening game at Cardiff's Millennium Stadium.
They were up against a US side buoyed by a historic midweek win on their World Cup debut against the Cook Islands.
During a scrappy opening five minutes, the Tomahawks had the Welsh pinned back in their own half and put them under early pressure.
Wales gained their composure and responded but full-back Rhys Evans was held up a yard from the try line during a promising spell.
There was a warning for Wales when the Tomahawks came within sight of the try line but the execution was wayward and the ball landed behind the advancing Bureta Faraimo.
But within a minute Wales made the breakthrough and a well-worked move saw Warrington Wolves wing Rhys Williams breaking down the left before releasing Roets.
Crusaders centre Roets touched down unopposed in the corner for the try, although Lloyd White failed with the conversion.
Wales' lead lasted barely three minutes and the ill-discipline which proved costly against Italy resulted in the Tomahawks' opening score.
Ian Webster conceded a penalty and a quick ball to the right found Joseph Paulo, who fed Newton to crash over the line.
Paulo failed to add the extras, but the Parramatta Eels stand-off was instrumental in his side's second try.
He took full advantage of space down the wing and his superb pass found wing Petersen to score in the corner, although Paulo failed with the conversion.
Wales emerged for the second half looking like a team eager to make amends for their disappointing first-half performance.
They piled on the pressure and White and Evans were held up by a dogged US defence.
Having weathered a heavy spell of Welsh pressure, the Tomahawks responded with their third try of the afternoon.
Full-back Evans fumbled a high ball and Paulo took advantage to cross over unchallenged, although he failed with the conversion.
It was a good spell for the Tomahawks, who were far sharper than Wales, and they were rewarded with a fourth try on the hour.
Samoa took full advantage of Wales' defensive frailties and dragged several players with him over the try line - the video referee called to confirm he had placed the ball down correctly.
Paulo succeeded with his first conversion of the afternoon before Newton scored his second try of the game.
Craig Priestly broke forward and he found Newton in support to score a fifth American try, which was converted by the impressive Paulo to extend the lead to 20 points.
Wales' World Cup dreams were slipping away and their afternoon was summed up when Kear, in sight of the try line, knocked on.
However, the hosts rallied in the final 10 minutes and were rewarded with two tries.
Kear fed Roets, who ran in clear from the halfway line, for his second try of the game before White successfully converted.
Two minutes later Anthony Walker, a debutant off the bench, chased a kick through by Peter Lupton to ground a try, which was only confirmed after being referred to the video referee.
White added his second conversion of the game before Wales came close to adding a third try in what was a rousing finale.
However, lock forward Ben Flower was held up a yard short of the try line and Wales' late comeback came to nothing.
Terry Matterson's US side face Scotland in Salford on Thursday and they will be confident of advancing to the quarter-finals after two wins out of two.
Wales will contemplate what might have been when they conclude their World Cup campaign against the Cook Islands in Neath next Sunday.
Wales: R Evans, Kear, Webster, Roets, Williams, White, Seamark, Kopczak, Budworth, James, Patrick, Frizell, Flower.
Replacements: Dudson, B Evans, Lupton, Walker.
USA: Freed, Faraimo, Tagaloa, Welch, Petersen, J. Paulo, Priestly, Offerdahl, Luani, Pettybourne, Newton, Shipway, D. Howard.
Replacements: Samoa, Hifo, Lavulo, Soloai.
Referee: Ben Cummins (Australia).