Nam, world No 635, came from behind to beat Lee Jea Moon of the Republic of Korea, world No 890, 3-6, 7-6, 6-1 in the second round.
The match lasted 2 hours and 23 minutes.
The match proved tough for Nam, even though his rival trailed him by more than 200 positions in the rankings.
In the next round, Nam, who won the 2015 Wimbledon Championships-boys’ doubles along with his Indian partner Sumit Nagal, will meet Sho Katayama of Japan, world No 623, who beat No 3 seed Niki Takuto.
Nam and his teammate Okamura Issei of Japan also entered the men’s doubles’ semi-final after beating Yuhei Kono and Yuto Sakai of Japan 2-1.