Courts Young Lions
Commanding a starting spot and impressing the coaches, Ong caught the eyes of the national youth setup. He then moved to Courts Young Lions as part of the Sea Games Preliminary Squad during the mid season transfer window. National Service commitments meant that Ong was ruled out of the Sea Games and was enlisted to the Army on 3 November 2011. Subsequent years followed in the S.League with the Courts Young Lions, however, appearances were limited due to NS commitments. In 2013, Ong was reunited with then 2011 Hougang United coach Aide Iskandar. He then started the season as first choice centre back for the Courts Young Lions, making 7 appearances before suffering an ACL injury and was ruled out of the season.