 Pamakwikwi eOlympics yeZhizha ya2004 muAthens, Ong akapfupisa purogiramu yake, achishambira mumitambo miviri bedzi yomunhu oga. Akabvisa FINA B-standard yekupinda nguva ye23.49 50 m freestyle kubva kuMalasian Open Championships muKuala Lumpur, uye 51.57 100 m freestyle kubva kuSoutheast Asian GamesmuHanoi, Vietnam. Mu 100 m freestyle, Ong akashora vamwe vanoshambira vanomwe mumakwikwi mana, kusanganisira vamwe vake vakakunda maOlympics kaviri Alexandros Aresti wekuCyprus naGeorge Gleason wekuVirgin Islands. Akapfuura Raichin Antonov wokuBulgaria kuti atore nzvimbo yechinomwe uye yechishanu yose ne 0.29 yechipiri, kunze kwekunyora kwake nguva ye52.04. Muchiitiko chake chechipiri, 50 m freestyle, Ong akaenzana nenzvimbo yake yechimakumi mana nenhanhatu yakabatana nemukwikwidzi weSEA Games Arwut Chinnapasaen pamatangiro emangwanani. Achishambira mumakwikwi mashanu, akakwanisa kuwana nzvimbo yechishanu mumasekonzi 23.52, achingova 0.03 yechipiri kubva panguva yake yokutanga. 