Jeonbuk made an early step to the top of the table with a 3-1 win over Daejeon Citizen - the best result of the season's opening weekend.
Leonardo set them on their way in the fifth minute, Lee Dong-gook doubled the lead before half-time and Kevin Oris added a 70th-minute clincher before Jeong Shung-hoon pulled a goal back late on.
Suwon Bluewings beat Seongnam Chunma 2-1. Seo Jung-Jin's early opener was cancelled out by Hwang Eui-Jo but Cho Dong-geon scored the winner in the 72nd minute.
Gangwon FC came from 2-0 down to draw 2-2 with Busan I'park, who seemed in control after Lim Sang-Hyub's first-minute goal and Park Jong-woo's penalty early in the second half. But Ianis Zicu quickly cut the deficit, also from the spot, before Bae Sung-hyo levelled.
Incheon United and Gyeongnam drew 0-0 in Sunday's other game.