كتب : وكالات
Colombian midfielder Mauricio Molina handed the Asian champions an early lead but Wahda equalized through a goal from Brazilian striker Fernando Baiano in the 27th minute.
Seongnam's Australian captain Sasa Ognenovski needed three minutes to restore his side's advantage and Choi Sung-kuk added the third on 71 minutes.
Forward Cho Dong-geon completed the rout in the 71st minute nine minutes from time.
Seongnam will face European champions Inter Milan on Wednesday for a place in the tournament's final.
Europe and South America have been the only continents that had representatives in the World Cup final since the tournament was introduced in 2000.