No 7 seed Nam retired due to injury whiletrailing to world No 844 Francis Casey Alcantara of the Philippines, 4-6,1-4.
Earlier, Nam beat Sho Katayama of Japan 6-2, 6-4in the first round.
In other news, Nam rose 43 places in the latestAssociation of Tennis Professionals men’s singles rankings.
Nam advanced from world No 601 to 558, bestranking of his career and the highest a Vietnamese player has ever ranked.
Nam improved his position after reaching thesemi-finals of the men’s singles category of the Singapore F1 event.
Nam will take part in the Singapore F3tournament on June 5. -VNA