The Baby Manu trailed 24-0 after just 15 minutes and were 31-7 behind at half-time in the playoff for 11th place.
Samoa twice managed to cut the deficit to 17 points in the second half but yellow cards to Godinet Foto Tinei and Theodore Avei Solipo at one stage reduced them to 13 players as Argentina eventually ran in seven tries to six.
The Baby Pumas led 53-28 before Tagaloa Tavita Fonoti and Alexander Pohla-Murray scored two consolation tries in the final minutes of the match.
Samoa were also beaten by England, Australia and Wales in pool play, and Ireland in the first round of knockout matches.
Meanwhile New Zealand were crowned Under 20 World Champions after thrashing England 64-17 in the final.