Dejan Stankovic (on foto) (121.36 points FTBL reiting) and skipper Javier Zanetti's first-half goals set the Nerazzurri on their way before Diego Milito sealed the result on 73 minutes.
Inter will now meet surprise package TP Mazembe in Saturday's final after the DR Congo side became the first African team to reach the title decider following their 1-0 win over Internacional on Tuesday.
Inter will be short-priced favourites to win the match and claim a fifth title of 2010 after a remarkable year that has seen them already win the UEFA Champions League, Serie A, Coppa Italia and Super Coppa.
Tarnished
The Italian club's win over Seongnam was, however, slightly tarnished by an injury to playmaker Wesley Sneijder who was forced off after just four minutes.
Rafa Benitez's side were already ahead at that early stage though after Stankovic ran onto a loose ball and fired a low shot across Jung Sung-ryong from just inside the area.
Inter went further ahead just after the half-hour following a neat one-two between Zanetti and Milito.
Zanetti slid a low pass into the area for Milito who back-heeled the ball back into the path of his fellow Argentine, who had continued his run, to thrash another low shot across the goalkeeper.
The South Koreans threatened a reply only on occasion, with Mauricio Molina twice shooting wide, before Milito ended the contest when he poked home after Samuel Eto'o had seen a shot saved.
© FTBL.com