Samoa opened the scoring in the first spell with a try to Faosiliva after the Pacific Island side were given a controversial penalty at the ruck.
Despite the tournament being held in Las Vegas the Samoans had a huge following with numerous red and blue flags popping up in the crowd.
The Kiwis hit back through the pacy Charles Piutau, but two more Samoa tries had the underdogs in front at the split.
New Zealand battled in the second spell but failed to hold the ball for long enough periods to assert any dominance on the game against a bruising Samoan side.
Their late fireworks made the game interesting but Samoa just had more strike power when it mattered.
New Zealand's road to the final was paved via a semifinal win against South Africa 20-7 and a grinding 12-7 quarter-final victory over England.
The Kiwis made their way through pool play with victories over Samoa, Australia and Japan.
After Samoa finished second in Pool A they powered to the showpiece game with a 19-14 quarter-final win over Kenya and a come-from-behind 14-12 semifinal victory over Fiji.
Fiji finished third with a 21-15 win over South Africa in the bronze final.
Samoa 26 (Alafoti Faosiliva 2, Paul Perez, Faatoina Autagavaia tries; Reupena Levasa 3 cons) New Zealand 19 (Ardie Savea, Tomasi Cama, Charles Piutau tries; Cama 2 cons) HT: 12-5
APNZ sports writer Daniel Richardson travelled to Las Vegas courtesy of Air New Zealand