Kammala jumla mai zuwa: An kammala karatunsa daga Makarantar Sakandaren Hyundai a Seoul, a cikin 2018 ya sanya hannu kan kwantiraginsa na farko tare da kungiyar K League 1 Ulsan Hyundai. Da farko an saita shi ne don karfafa tawagar matasa na "Horangi" a cikin wasannin ajiya na kasa: duk da haka, a ranar 1 ga Maris, 2018, manajan Ulsan Kim Do-hoon ya ba kowa mamaki ta hanyar ba Oh babban jami'in sa na farko yana da shekaru 19 kawai, yayin da ya zaɓe shi don farawa XI a kan Jeonbuk Hyundai Motors a wasan farko na
lokacin. Ya buga minti 56 kafin Júnior Negrão ya maye gurbinsa, kuma ƙungiyarsa ta sha wahala daga 2-0.