Two home sides with clear territorial control, each against opponents with problems at the back.
Ulsan has played most of its home games as high-scoring affairs, concedes a lot of shots on target, and comes in with long rest against a Gangwon side on a short turnaround. Ulsan controls the ball and shoots often, and Gangwon's volume means it should get a goal back. I'm siding with a game of plenty of goals.
Suwon is third in its table and Ansan is fifteenth, with Suwon conceding far less and dominating possession. Its only recent loss came from an own goal despite twenty shots, which says finishing rather than collapse. It won at Ansan earlier in the season. That's why I'm siding with Suwon to win.