First-choice goalkeeper Jung Sung-Ryong was named in the Korea net after recovering from injury and was called into action on 25 minutes.
A long-range strike from Hiroshi Kiyotake's forced Jung to push the first real chance of the match wide.
Hiroki Sakai went close for Japan, but he headed Kiyotake's corner wide just moments before Park gave Korea a 38th-minute lead.
The Arsenal striker latched onto a long punt forward before dodging the challenge of two Japanese defenders and striking low into the bottom corner.
Korea nearly doubled their advantage before the break, but Yun Sukyoung's shot narrowly missed the post.