Tonga had scored 38 unanswered points by half-time and continued to dominate after the break, with a Hong Jun-ki penalty all the South Koreans could muster.
A plethora of players helped themselves to tries for Tonga as they made light work of the Koreans.
Vaea Poteki scored a hat-trick of tries while Hudson Tonga'uiha touched down twice, as did fly-half Fangatapu Apikotoa, who also made 10 conversions.
Sione Fonua, Hale T. Pole, Teu'imuli Kaufusi, Vungakoto Lilo, Heamani Paea and Sione Kalamafoni all got one try each.
Tonga will join England, South Africa, Samoa and the United States in Pool A at the World Cup.