Kim Bong-Gil's men have now lost three consecutive league matches and find themselves bottom of the table, already five points adrift of their nearest rivals.
Their task was always going to be tough on Sunday against league leaders Pohang, and Shin Kwang-Hoon put Incheon on the back foot when he opened the scoring in the 16th minute.
Kim Gwang-Seok and Lee Myeong-Ju added two goals in the final five minutes to complete the victory and record Pohang's fourth win in a row, while Stefan Nikolic was dismissed for the strugglers with three minutes to play.
Jeonbuk Motors remain two points behind Pohang in second place after their 4-1 win over Gyeongnam, with Lee Dong-Gook netting his fourth goal of the season from the penalty spot.
Third-placed Jeju United collected a 2-1 victory against Busan I'Park, although they had to come from a goal behind to secure the three points thanks to Yoon Bit-Garam and Jin Dae-Sung.
Jeonnam Dragons' topsy-turvy campaign continues as they put last week's defeat to Jeonbuk behind them with a 1-0 win over struggling Seongnam.
They were made to wait though, with Lee Jong-Ho converting the only goal of the game with six minutes to play to keep them in touch with the top three.
Despite having just a solitary win to their name this season, Sangju Sangmu extended their unbeaten run to four games with a 1-1 draw against Ulsan, a result that leaves the latter five games without winning after Kim Yong-Tae cancelled out Lee Jung-Hyub's opener for Sangju.
Meanwhile, Seongnam dropped to second bottom after their defeat as Seoul recorded a 1-0 victory over Suwon Bluewings.
Japanese midfielder Sergio Escudero struck the winning goal as last season's AFC Champions League runners-up took advantage of all their rivals failing to win.
