Suwon bag points, Steelers hit five
After 14 minutes, Stevica Ristic latched on to a Yeom Ki-Hoon header to break into the Seongnam area, hold off the challenge of a defender and fire a low shot past Ha Kang-Jin.
Ten minutes later, Park Hyun-Beom made it to the left touchline and his low cross was flicked home by Yeom from close range.
Seongnam dominated much of the rest of the match and were back in the game early in the second half as Sasa Ognenovski headed home from a Hong Chul free-kick.
Midway through the second half, Cho Dong-Keon was brought down in the area but saw his spot-kick well saved by Jung Sung-Ryong.
With five minutes left, Oh Jang-Eun sealed the win with a glancing header, although Ognenovski scored again in the closing seconds.
"This was a big step for us in our bid to finish in the top six to enter the play-offs," said Suwon coach Yoon Sung-Hyo, who saw his team maintain their fourth position. "There is still work to do but it was important to win today."
Pohang Steelers moved to within seven points of leaders Jeonbuk Motors by thrashing Gwangju FC 5-1. Mota and Koh Moo-Yeol both bagged braces, with Noh Byung-Joon getting the fifth. Park Ki-Dong got a consolation for Gwangju.
Ulsan Horang-I kept their play-off hopes alive with a 2-1 win at Jeju United thanks to a brace from defender Kwak Tae-Hwi. Santos got the goal for the hosts.
Elsewhere, Gangwon FC picked up their second win of the season, beating Sangju Sangmu 2-0 with Seo Dong-Hyun getting an early goal and Jung Sung-Min a late one.