Portugal, needing only a draw to be sure of top spot in Group H and mindful of the risk of yellow-card suspensions in the next round, have brought Diogo Dalot and Antonio Silva into the defence.
Matheus Nunes, Vitinha and Joao Mario come into the midfield in place of Bernardo Silva, William Carvalho and Bruno Fernandes -- who scored twice in the 2-0 win over Uruguay -- while Ricardo Horta replaces Joao Felix up front.
South Korea's Portuguese coach Paulo Bento left out central defender Kim Min-jae, who was an injury doubt, and replaced him with Kwon Kyung-won, while Lee Jae-sung and Lee Kang-in were drafted into midfield.
The Koreans, with one point so far, must beat Portugal and hope the result of Ghana's match with Uruguay goes their way in order to reach the last 16.
TeamsSouth Korea: Kim Seung-gyu, Kim Moon-hwan, Kwon Kyung-won, Kim Young-gwon, Kim Jin-su, Lee Jae-sung, Lee Kang-in, Jeong Woo-yeong, Hwang In-beom, Son Heung-min, Cho Gue-sungPortugal: Diogo Costa, Diogo Dalot, Pepe, Antonio Silva, Joao Cancelo, Matheus Nunes, Ruben Neves, Vitinha, Joao Mario, Cristiano Ronaldo, Ricardo HortaWriting by William Schomberg and Anita Kobylinska; Editing by Ken FerrisOur Standards: The Thomson Reuters Trust Principles.