First-half goals from Yang Sang-min and Ha Tae-goon set the visitors on their way, with further strikes from Seo Jung-jin and Everton putting the result beyond doubt before Kim Eun-jung's late penalty consolation.
The triumph moved the Bluewings two points ahead of FC Seoul, who host Ulsan Hyundai.
There were also emphatic victories for struggling duo Gwangju FC - 6-0 against Chunnam Dragons - and Daejeon Citizen, who were 3-0 winners at Seongnam Chunma.
Gwangju had their match wrapped up by the interval, with Park Min and Kim Dong-sub grabbing two goals each and Kim Eun-sun also on target in the first half before Joao Paulo sealed the rout in the 64th minute.
Daejeon also assumed control early on, Kevin Oris and Kim Hyeung-bum putting them two up within 14 minutes before Kim Tae-yeon completed the scoring six minutes after the break.
Fourth-placed Jeju United lost ground on the leaders as they went down 1-0 at home to Pohang Steelers, Lee Myung-joo netting the game's only goal six minutes from time.
Finally, Incheon United claimed only their second win of the campaign - 1-0 against Sangju Sangmu Phoenix thanks to Seol Ki-hyeon's last-gasp goal - but it was not enough to lift them off the foot of the table.