The New Zealand under-20 side have finished fourth at the World Championships for just the second time after losing the bronze final to South Africa 40-30.
The Baby Blacks scored three first-half tries to lead 25-14 at halftime before South Africa took control of the game in the second half.
South Africa scored 26 unanswered points with four second-half tries.
Second-five Harry Plummer top-scored for New Zealand with a try, two conversions and two penalties but it wasn't enough.
It is not New Zealand's worst mistake at the Under-20's, finishing fifth in 2016 after failing to qualify for the semi-finals.