The Men in Blue opened the score board scoring three consecutive tries in the first five minutes.
The tries were scored by Tanu Niulevaea, Paul Eti Slater and Owen Niue.
The Brian Liman coached side continued to break the defence line of the South Africans to score one more try and led 26-0 at halftime.
Samoa continued to score three more tries in the second half before South Africa scored the last and lone try of the match.
Samoa will now face Great Britain in the final of the 5th place play-off.