Noh Byung-joon struck the only goal of the game eight minutes from time as Pohang moved a point above Ulsan Hyundai, who were held 2-2 at Incheon United.
It might have been even worse for the former leaders after they found themselves 2-0 down after just 31 minutes to goals from Seol Ki-hyeon and Park Tae-min, but the visitors battled back to salvage a draw with second-half efforts from Kim Chi-gon (52) and Rafinha (62).
Third-placed FC Seoul also took advantage of Ulsan's slip to move to within six points of second spot with a 2-1 win over Suwon Bluewings.
Seoul took a 2-0 lead through Adilson (30) and Kim Jin-kyu (54) and that was enough to earn the reigning champions a fifth successive win despite Suwon pulling a late goal back through Cho Ji-hun.
Elsewhere, a hat-trick from Lim Sang-hyub helped Busan I'Park to a 5-1 home win over Gyeongnam. Lim struck in the 28th, 40th and 66th minutes while Park Yong-ho (51) and Park Jong-woo (71) were also on the scoresheet for the victors. Lee Jae-an netted an 80th-minute consolation for Gyeongnam.
In today's other game, Jeju United and Chunnam Dragons shared a goalless draw.