Choi Yong-Soo’s men have now won their last seven league games to earn their place in the championship round, impressively seeing off a late comeback from Daejeon.
With the hosts seemingly cruising, Kim In-Wam's strugglers fought back from 2-0 down to level through Jin-San Hwang in the 87th minute.
But their hard work was undone deep in stoppage time when defender Ko Yo-Han found the back of the net to rob the three points and seal their place in the Championship round.
Jeonbuk clinched the vital points after their visitors could not cancel out Lee Seung-Ki’s 48th-minute goal.
While bottom club Daejeon's woeful form continues ahead of the relegation play-offs, Busan I’Park and Incheon United moved one step closer to finishing in the top half of the table on Sunday.
Busan just clinched victory against Ulsan with an 83rd minute goal from Rodrigo Da Costa to keep their Championship hopes alive after a number of early draws in the season gave them an uphill task.
They face Jeju in their next game hoping to overtake them after Park Kyung-Hoon's side were held 1-1 by Daegu, moving the 1989 champions within a point of the top seven.
Incheon United have also struggled with patchy form which they remedied with a 2-1 win away to Gangwon, despite them being 1-0 down all the way through to the 80th minute.
The game was turned on its head when 23-year-old Diogo Acosta fired home a penalty, to mark his sixth goal of his debut season, before Ahn Jae-Joon rippled the back of the net ten minutes later.
The weekend also saw a number of draws with league leaders Pohang Steelers unable to break Gyeongnam.
The points were also shared in Suwon Bluewings contest with Seongnam on Saturday with Cho Dong-Geon's brace for the home team just not quite proving enough.
