Ulsan face their biggest test yet in the K-League with a visit to Jeonnam Dragons, while four teams search for their first wins.
Coach Cho Min-Kook's league-leading Ulsan side have made the perfect start to the campaign with three wins from as many games.
They are yet to concede and have scored seven times to be two points clear with the only 100 per cent record in the league.
Kim Shin-Wook has led the way up front with a league-best three goals for Ulsan, who last won the league title in 2005 but were runners-up last year.
But none of their wins this season have come against teams sitting in the top six, with their latest victory a 3-0 thrashing of bottom side Incheon United on Sunday.
Jeonnam Dragons are third after two wins from three, with Macedonian striker Stevica Ristic and former Porto winger Leandro Lima sure to play key roles on Wednesday.
Jeonbuk Motors will be ready to pounce if Ulsan slip-up, with Choi Kang-Hee's men hosting Pohang Steelers.
Choi's side are yet to concede in the league this season and would be level on points with Ulsan if not for a 0-0 draw at Sangju Sangmu last time out.
There are four teams who are yet to win, including 2010 and 2012 champions Seoul.
Seoul host fourth-placed Jeju United hoping to kick-start their campaign after a slow start, which has seen them collect just one point.
Without last season's equal top goalscorer in Dejan Damjanovic, who left for Chinese Super League side Jiangsu Sainty in December 2013, Seoul are without a league goal in three matches.
Incheon United are bottom, also on one point, ahead of their trip to Gyeongnam, while also-winless Seongnam host Suwon Bluewings.
Sangju Sangmu are winless and unbeaten after playing out three draws to start the season, and they visit Busan I'Park.