Thanks to a 4-1 win over Shandong Luneng at Jeonju World Cup Stadium in Jeonju, North Jeolla Province, Jeonbuk finished second in Group E with 11 points. Jeonbuk joins three other K League Classic sides in the round of 16. The top South Korean league last put four teams in the knockout stage in 2010.
Earlier Wednesday, Seongnam FC lost to Gamba Osaka 2-1 to finish as Group F runner-up. Seongnam had already booked a knockout berth two weeks ago.
Suwon Samsung Bluewings and FC Seoul are the two other K League Classic clubs to have qualified for the next round.
In Jeonju, Jeonbuk only needed a draw to move on, but piled on Shandong with four goals from four different players.
Lee Jae-sung headed in the opening goal in the 25th minute.
Wang Tong drew Shandong even near the end of the first half, but that turned out to be the only offense for the visitors.
Kim Hyung-il scored on a header six minutes into the second half. Eninho converted a penalty in the 80th minute and Edu put the icing on the cake with Jeonbuk's fourth goal in the 88th.
Jeonbuk will face Group G winner Beijing Guoan in the home-and-away round of 16, first on May 19 and then on May 26.
At Expo '70 Stadium in Osaka, Gamba Osaka won the group with the come-from-behind win. Gamba Osaka, Seongnam and Buriram United all finished with 10 points but the first two clubs advanced thanks to a tiebreaker edge.
As the second seed in Group F, Seongnam will face Group H winner Guangzhou Evergrande in the home-and-away round of 16. The two matches will be held on May 20 and May 27.
Hwang Ui-jo put Seongnam on the board in the 15th minute, as his shot went in off an opposing defender.
Hwang left the match near the end of the first half with a left thigh injury. Then, three minutes into the second half, Seongnam lost another player, with defender Kim Tae-youn injuring his right thigh trying to foil a breakaway.
Gamba Osaka took advantage and drew even in the 64th minute with Takashi Usami's goal.
Lins got the winner for the home team in the 82nd minute, capitalizing on Seongnam's shoddy defense. (Yonhap)
