Yong-Soo Choi's men now sit just one point behind Jeonbuk and a spot in the top three thanks in the main to striker Dejan Damjanovic, who notched up an impressive hat-trick.
The Montenegro international now has 16 league goals this season and his treble keeps his side in the hunt for an automatic return to the Champions League after they were beaten by Guangzhou Evergrande in this season's final.
It took Damjanovic just five minutes to open the scoring at the Seoul World Cup Stadium and he doubled his tally just a minute after half-time.
Mauricio Molina then made it three on 54 minutes before Damjanovic rounded off his hat-trick seven minutes from time.
Park Se-Jik pulled one back for the visitors in the 89th minute, but this served as no more than a consolation.
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