Ulsan moved ahead of Pohang Steelers at the top of the K-League with a 1-0 win over Busan I'Park.
Rafinha sealed the points for the leaders with a 55th-minute strike, sending Busan to their 11th defeat of the campaign.
Pohang relinquished top spot after they were held by the Suwon Bluewings 2-2 at home.
A Kwak Kwang-Seon own goal in the opening minute gave Pohang the perfect start but they had to rely on a last minute Park Seong-Ho strike to earn a point.
Suwon had looked on the verge of victory after a second-half double from Jong Tae-Se, however they were denied a 14th win of the season by Park's 90th-minute leveller.
Incheon United extended their lead over Busan at the bottom of the Championship Round table to four points with a 0-0 draw against Seoul.
Seongnam remain top of the Relegation Round with a 2-1 victory over second place Jeju United.
The hosts opened the scoring in the opening minute through Lee Jong-Won.
Ahn Jong-Hoon levelled five minutes later, before Kim Dong-Sub won the game for Seongnam in the 10th minute.
Daejeon Citizen picked a crucial point in their battle to avoid relegation as they drew 1-1 with Daegu.
Derek Asamoah opened the scoring for Daegu in the 29th minute, but Joao Paulo snatched a point with an equaliser in with six minutes to play.
Gangwon also helped their fight against relegation with a 2-1 win over Gyeongnam.
Kim Bong-Jin and Kim Dong-Ki moved them into a two-goal lead, and although Yoon Shin-Young halved the deficit Gangwon held on to earn the three points.