The champion from the now-defunct Feather Weight division secured a 19-9 victory over his opponent from the Republic of Korea.
The bout was all but over after world champion Lomachenko won the first round 7-2 and although Han did well to lose the second only 4-3, normal service resumed in the final round, which he lost 8-4.
Russia's Egor Mekhontcev claimed the Light Heavy Weight gold after the tightest contest possible against Kazakhstan's Adilbek Niyazymbetov.
The bout was scored 15-15 and the fighters could not even be separated by countback, with Mekhontcev winning courtesy of the judges' individual preference.
Niyazymbetov edged the first round 4-3, with Mekhontcev taking the next 5-4 to draw level.
And it was 7-7 in the final round, prompting what was a dramatic conclusion.