Jeonbuk, which is aiming to win the K-League for 6 years in a row, lost to Jeju and lost 3 in a row.
Jeju Jumin-gyu scored one goal and one assist and knocked down Jeonbuk.
Jeju Gerso's cross is lightly connected by Jumin-gyu with a header to shake the net.
This is the first goal of the season by Jumin-gyu, the top scorer of last season.
Jeonbuk, aiming for a counterattack, was disappointed with Kim Jin-su's left-footed non-stop shot hitting the post in the 28th minute of the second half, and Jeju nailed it in the 35th minute.
When Jumin-gyu pierced a kill pass through the opposing defense, Kim Joo-gong finished with one-touch with his right foot.
Jeju, who won 2-0, defeated Jeonbuk for the first time in 4 years and 9 months, and Jeonbuk lost 3 consecutive losses.