K.League leaders Pohang Steelers were held to a surprise 0-0 draw by bottom club Incheon United on Wednesday.
The reigning champions would have been confident of recording their third straight league win against a side who have picked up just one victory all season.
However, a shock was afoot at Sungui Arena Park, as Incheon held their own to earn a hard-fought point.
Pohang's slip-up did not prove costly, though, as second-placed Jeonbuk Motors also drew a blank in their 0-0 stalemate at Ulsan.
Those results mean it is as you were at the K.League's summit, with Pohang remaining two points clear of Jeonbuk.
Jeju United were the main beneficiaries of the top two dropping points, as they leapfrogged Jeonnam Dragons into third spot with a 2-0 home win over Ha Seok-ju's team.
Park Su-chang opened the scoring at the Jeju World Cup Stadium after 19 minutes, before Australian defender Aleksandar Jovanovic made sure of a valuable victory late on.
Elsewhere, an ill-tempered affair between Seoul and Sangju Sangmu in the capital ended 2-1 to the hosts.
Sangju received seven bookings throughout the game - including two for Yoo Ji-hun, who was sent off just before half-time - and went ahead 12 minutes after the interval courtesy of Kim Chang-hoon.
However, the visitors' numerical disadvantage soon started to show, and Mauricio Molina drew Seoul level with his first goal of the season 20 minutes from time.
Seoul made sure of all three points when Sergio Escudero popped up with a late winner.
In Wednesday's other action, Suwon Bluewings further boosted their Championship Round credentials with a 2-1 win at Busan, and Seongnam beat second-bottom Gyeongnam 1-0.