Ryu's side were winning 2-1 in the best-of-five Team match when the Athens 2004 gold medallist faced Kim Hyok-Bong, who he last year played with at the Qatar Peace and Sport Cup.
Ryu was twice behind, but sealed the last two games 11-5 and 11-3 to deliver a success.
Meanwhile, Chinese competitors were beaten by non-compatriots in a match for the first time at the Games, but still progressed comfortably.
With China 2-0 ahead versus Russia, Ma Long and Wang Hao surrendered a 2-1 lead to lose their Doubles match against Alexey Smirnov and Kirill Skachkov 3-2.
Yet recently-crowned Olympic Games champion Zhang Jike restored order to seal China's 3-1 triumph by overcoming Smirnov.
Elsewhere, Japan and Singapore eased to 3-0 victories over Canada and Australia respectively.
Related content
- Athletes
KOR
PRK
- Sports
- Countries
