The hosts went ahead after 18 minutes through Eninho and made sure of the points 11 from time with a goal from Lee Dong-gook.
Jeonbuk stay one point ahead of FC Seoul, who were 2-1 winners over Gyeongnam.
Seoul trailed to a ninth-minute strike from Kim In-han, but hit back in the second half through Ha Dae-song (51) and Sergio Escudero (74).
Kim Seung-yong scored the only goal after 84 minutes as Ulsan Hyundai edged out Seongnam Chunma 1-0 to leave them seven points behind the top two.
Suwon Bluewings lost ground at the top, however, with a goalless draw at Busan I'park.
Gwangju FC climbed off the foot of the table with a 1-0 victory at home to Sangju Sangmu Phoenix - Jeong Woo-in grabbing the decisive goal 11 minutes from time.
A last-minute goal from Jair Da Silva earned Jeju United a 1-1 draw at Gangwon FC, who led through Bae Hyo-sung's 70th-minute strike.