The fourth seed, who has a rapid Elo rating of 2168, won the first six games including against Indonesian top seed Priasmoro Novendra (Elo 2263).
In the last and seventh game Khoi he agreed to a quick draw with India’s Raghunandan Srihari to finish the tournament with 6.5 points. He gains 30 Elo points.
Khoi enters the standard chess competition as the top seed with an Elo rating of 2516.
Last month he won two individual and two team gold medals in the U20 division at the 2019 ASEAN Age-Group Chess Championships in Mandalay, Myanmar.
The 2019 Asian Junior (Open and Girls) Chess Championship is taking place in Solo, Indonesia, from July 1 to 8, and features three categories, rapid, blitz and standard chess.
It has attracted 34 boys and 36 girls from Bangladesh, Hong Kong, Indonesia, India, Iran, Kazakhstan, Malaysia, New Zealand, the Philippines, Taiwan and Vietnam.