Overnight leader Yuka Saso of the Philippines slipped to third place on nine-under 207 after shooting an even-par 72 in the third and final round.

Atthaya had earlier shot a flawless seven-under 65 to lie just one shot behind Saso after the second round.

Atthaya became the youngest Ladies European Tour winner at only 14 when she won in Pattaya last July.

Tunrada Piddon finished tied 13th on 215, while Natthakritta Vongtaveelap was joint 20th.

However, Thailand will have to wait for at least another year for the team title after they finished runners-up to South Korea.

"It is disappointing because we were so close," said Atthaya after she was unable to lead Thailand to their maiden team title. "We just have to keep trying."

Atthaya (67) and Tunrada (71) combined to take Thailand to 15-under 417, matching the Korean effort of Jeong Yun-Ji (70) and Cho A-Yean (68).

But the honours went to the South Korean team, whose third player Lim Hee-Jeong shot an even-par 72, while Thailand's Natthakritta could only manage a 73.

The team event only counts the two best scores from the three members but in case of a tie, the third player's score is taken into account.

Japan came third on 418.

Top amateurs from 14 nations -- Australia, New Zealand, Indonesia, Singapore, Malaysia, India, Myanmar, Hong Kong, Taiwan, China, the Philippines, Japan, South Korea and Thailand -- took part in the event.