Leaders Jeonbuk came into Sunday's home clash with bottom side Gyeongnam as firm favourites, but they were made to work hard for maximum points.
Choi Kang-hee's men took 83 minutes to break the deadlock, as Kim Nam-il's late winner earned them a 1-0 success.
That result restored Jeonbuk to their position as league leaders after defending champions Pohang had moved top with a 1-0 win over Seongnam 24 hours earlier.
Ko My-yeol was the hero for the home side, netting the only goal of the game in the 63rd minute.
At the wrong end of the table, Sangju Sangmu ended their six-match winless streak in the league thanks to a 1-0 home win over Jeonnam Dragons.
Ho Lee was the match-winner, with his effort four minutes into the second period earning Sangju a first K-League victory since a 3-2 win at Jeju United in early August.
Jeju gained revenge for that defeat with a 2-1 win at Sangju last time out, a result that led head coach Park Kyung-hoon to claim that his side would get even better.
Park's prophecy fell flat on Sunday, however, as Jeju drew 0-0 with Suwon Bluewings.
Seoul warmed up for their AFC Champions League semi-final first leg against Western Sydney Wanderers on Wednesday in perfect fashion as Choi Yong-soo's men defeated 10-man Incheon United 3-1 in the capital.
Yun Ju-tae opened the scoring in the 27th minute and the advantage was doubled by Choi Jung-han's effort four minutes before the interval.
Kim Jin-kyu's penalty six minutes after the break put the result beyond doubt, and, despite seeing Lee Chun-soo sent off, Incheon did manage a last-minute consolation through Lee Hyo-gun.
Elsewhere, Ulsan came from behind to see off Busan I'Park by the same scoreline.
Busan had gone four games without a win prior to this encounter, and must have thought things were looking up when Lee Kyung-ryul put them ahead in the 49th minute.
It was not to be, however, as goals from Baek Ji-hoon, Kim Sung-hwan and An Jin-beom wrapped up the points for the visitors.
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