South Korea retained their crown with a 2-1 victory over Japan in Hangzhou, having conceded a goal in only the second minute.
But livewire Lee, 22, who joined PSG from Mallorca in the summer, rallied his team and they got back on level terms midway through the first half.
In a competition featuring under-24 squads plus three overage players, Cho Young-wook scored the winning goal soon after the break to extend South Korea's dominance with their sixth overall title.
Nearly every able-bodied South Korean male is required to perform at least 18 months of military service, but the government rewards Asian Games gold medals and Olympic medals of any colour with an exemption.
South Korea lined up for the final with several players from European clubs while Japan fielded a team mostly drawn from the domestic J-League.
Attacking midfielder Lee had been used sparingly by the Koreans since arriving late in China but he took his place in the starting XI.
Japan got off to a sensational start when Kotaro Uchino gave them the lead with less than two minutes on the clock.
Kein Sato darted down the left and played in a cross that Masato Shigemi nudged on to Uchino to fire home.
South Korea took control of the game, with Lee pulling the strings, but they struggled to convert their dominance into scoring chances.
That was until Jeong Woo-yeong notched the equaliser in the 27th minute, jumping above defender Manato Yoshida to head home Hwang Jae-won's cross.
It was the Stuttgart forward's competition-leading eighth goal of the tournament.
South Korea continued to press and got their reward in the 56th minute.
Hwang surged forward and prodded the ball through to Jeong, who gave it to Cho to fire home.
South Korea had several chances to extend their lead but Japan rarely threatened.
Uzbekistan beat Hong Kong 4-0 to win the bronze medal.
