Park He-do scored on the half-hour mark as the leaders took a huge step toward the title.
They were boosted by Jeonbuk's 3-0 home defeat to Pohang Steelers, who took the lead through Kim Dae-ho in the 24th minute and doubled their advantage through the same player 10 minutes after the break. Park Sung-ho added a third a minute later.
In the relegation round, Daejeon Citizen's Alex Terra and Gangwon FC's Ianis Zicu's both scored hat-tricks as Daejeon claimed a 5-3 victory.
A Terra double and a Kevin Oris goal had the hosts 3-1 up at the break and, even though Gangwon came back to 3-3, Terra completed his treble and Han Kyung-in sealed the win.
Daegu FC battled from 2-0 down in the last six minutes to draw 2-2 at Chunnam Dragons.
The Dragons looked on course for a routine triumph when goals from Joo Sung-hwan and Ko Cha-won put them 2-0 up. But Choi Ho-jung pulled one back in the 84th minute and Hwang Il-soo levelled in the last minute.