The leaders began the day with a two-point lead over reigning champions Pohang Steelers and enhanced their position at the summit with a 2-0 win over Jeju United.
Goals in the opening six minutes from Kim Dong-chang and Lee Dong-gook put Jeonbuk in complete control of proceedings and there was no way back for Jeju.
Pohang, meanwhile suffered a shock 2-1 defeat at lowly Gyeongnam.
After a tight opening hour the deadlock was broken on 62 minutes when Lee Jae-an gave Gyeongnam the lead.
Ko Mu-yeol levelled with six minutes remaining and looked to have sealed a point for Pohang, but Lee Chang-min secured all three points for the hosts as he netted a 93rd-minute winner.
Suwon Bluewings also dropped points and now sit level with Pohang following a 1-1 draw with Incheon United.
Junior Santos struck his 10th goal of the season to give Suwon the lead early in the second half, but that advantage lasted only six minutes as Choi Jong-hwan earned Incheon a share of the spoils, extending their unbeaten run to three games.
Seongnam, who had been one of three sides level at the foot of the table together with Gyeongnam and Busan I'Park, recorded a 1-0 victory over Jeonnam Dragons courtesy of Kim Dong-hee's 49th-minute strike.
Busan were held to a 1-1 draw by another struggling side, Sangju Sangmu, with both sides slipping below Seongnam and Gyeongnam in the table as a result.
A second successive victory appeared set to come Busan's way before Baek Jong-hwan snatched a late equaliser for Sangju Sangmu.
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