Despite being the sport's dominant nation for well over 20 years, the men's gold had so far eluded Republic of Korea, whose prospects took a blow earlier in the day when top seed and hot favourite Im Dong-hyun was knocked out.
A third from the nation, second seed Kim Bubmin, also bowed out before the medal matches as he was defeated 6-5 by China's Dai Xiaoxiang, but Oh shot nervelessly to ensure a third gold from a possible four for his country at London 2012.
Furukawa took silver and Dai bronze, his country's first Individual men's medal, after seeing off the Netherlands' Rick van der Ven in yet another shoot-off.
Van der Ven, looking to replicate his coach Wietse van Alten, who finished third at Sydney 2000, produced the upset of the day to take out Im in the last 16.
But he was edged off the podium when Dai settled their match with a 10 in the one-arrow decider.
Having finally achieved his Olympic dream, Oh is now desperate for more of the same.
'I think maybe I was not as good in my 20s as I am now, but having turned 30 I am better and I want continue in this sport a long time,' he said.
'I have been in the national qualifiers since Sydney so I always hoped to participate in an Olympic Games, let alone get a medal.
'My first dream came true by being here and on top of that I have a gold medal so I am a very happy man.'