Leandro Lima opened the scoring in the 36th minute and Dinelson made it two just after the hour mark.
Fourth-placed Jeju remained six points behind third-placed FC Seoul and seven off leaders Jeonbuk Motors, having played a game more than the top three.
Park Yong-ho scored twice as Busan I'Park beat Daejeon Citizen 3-1.
Park scored scored in the fourth minute and put his side 2-1 up in the 76th minute after Yuta Baba levelled from the spot before the break.
Han Jeong-hwa sealed the points for Busan eight minutes from time.
Wesley scored an 84th-minute winner to earn Gangwon FC a 2-1 win at Seongnam Chunma.
Kim Eun-jung put the visitors in front, but Kim Sung-hwan levelled early in the second half.
In the day's other game Gyeongnam and Incheon United drew 0-0.