The 19-year-old Chennai lad overcame the unseeded Korean 3-6 7-6(6) 6-4 in the fiercely-fought final at VIPS Club.
It was Ramkumar's third final of the career and second of the season.
He had lost to Canadian Steven Diez in Spain in June this year. Last year in December he lost to compatriot Sanam Singh in the Dharwad.
With his much improved show, Ramkumar has staked his claim for a wild card entry into Chennai Open, country's only ATP 250 event, starting next month.
Former national champion Jeevan Nedunchezhiyan, who won one title and ended runner-up in four others, is also a strong contender, according to a TNTA source.
Coimbatore player N Sriram Balaji, who won two singles title this season is also a contender.