Suwon Bluewings closed the gap on K-League leaders Jeonbuk Motors to two points following a 2-1 win over Chunnam Dragons.
Santos scored in the final minute for the Bluewings after his opener in the 14th minute had been cancelled out by Leandro Lima just after the hour mark.
Third-placed Pohang Steelers fell five points behind the Bluewings following a 2-1 defeat at Incheon United.
In a frantic opening, Lee Chun-Soo opened the scoring in the fifth minute with Ko Mu-Yeol levelling for the Steelers five minutes later before Jin Sung struck eight minutes from time to give Incheon victory.
Jung Sung-Ho's strike midway through the first half and Kim Tae-Hwan's 80th-minute effort gave Seongnam Chunma a 2-0 win at Gyeongnam.
Source: FIFA.com