Incheon United and Jeju United both moved to 11 points from six games played in the K-League, with victories on Saturday.
Incheon won 3-1 away at struggling Daegu, with Lee Seok-Hyun, Han Gyo-Won and Ahn Jae-Joon the goal-scorers for the visitors at Daegu Main Stadium.
Kim Bong-Gil's men sit fourth on the table, level on points with third side Jeju - after the latter put Gangwon to the sword, winning 4-0. Pedro Junior struck a double for the hosts at Jeju World Cup Stadium, adding to Heo Jae-Won's opener before Bae Il-Hwan topped off the win with their fourth strike of the contest.
Chunnam Dragons enjoyed their first victory of the season with a 3-1 triumph at home to Daejeon Citizen.
Kim Dong-Cheol, Jeon Hyeon-Chul and Sim Dong-Woon were all on target for Chunnam.
Gyeongnam were held at home to league leaders Pohang Steelers in a 1-1 draw, the former's fourth consecutive stalemate.
Both sides are unbeaten this season, but Gyeongnam are seventh on the table, four points behind Pohang.
Ulsan missed the chance to go top of the table, instead they sit fifth, after being held to a 0-0 draw at home to Busan l'Park.
They did, however, move level with each of Incheon and Jeju on 11 points, and are just one point off leaders Pohang.