The victory puts daylight between the leaders and second-placed Pohang Steelers, who were held 1-1 by Daegu yesterday, and leaves 2010 AFC Champions League winners Seongnam just one place off the bottom.
Jeonbuk took the lead in a slightly fortuitous fashion in the 16th minute when Krunoslav Lovrek cut into the area near the byline and his low cross hit the chest of visiting defender Jeong Ho-jeong before spinning into the Seongnam net, giving the goalkeeper no chance.
After the break, Seongnam pushed forward in search of an equaliser and almost got it after 55 minutes when Brazilian striker Emerton headed against the crossbar from close range.
Jeonbuk made the most of that let-off by extending their lead just after the hour in simple fashion.
Lee Dong-gook chested down a high ball on the edge of the area and slipped a pass through to Kim Dong Chan, who, loitering on the penalty spot, turned and side-footed home to seal the win.
"It was a tough match as we expected," said Jeonbuk coach Choi Kang-hee. "We could have played better but we did what we had to do."