The 21-year-old Kunlavut, a former world junior champion, stunned world No.1 Viktor Axelsen 22-20, 10-21, 21-12 in the 64-minute decider at KD Jadhav Indoor Hall.
Kunlavut, who won his first Super 300 event at the German Open last year, finally got the better of his illustrious opponent after losing all of their six previous meetings including three finals.
Kunlavut received $59,500 (approx B1,933,000) while Axelsen got $28,900 (B939,000).
Olympic and world champion Axelsen, who won the India Open in 2017 and 2019, claimed the season-opening title at the Malaysia Open in Kuala Lumpur last week while Kunlavut made it to the semi-finals.
The women’s singles crown went to An Se-Young of South Korea.
The Korean second seed claimed a sweet revenge against world champion Akane Yamaguchi of Japan with a come-from-behind victory in the women’s singles final.
An rallied from one game down to beat the top seed 15-21, 21-16, 21-12 in 62 minutes.
Yamaguchi beat An in the final in Malaysia a week ago.
It was their sixth career final and 16th face-off overall. Yamaguchi now leads their head-to-head 10-6.
Liang Weikeng and Wang Chang of China took home the men’s doubles title.
The unseeded Chinese pair defeated third seeds Aaron Chia and Soh Wooi Yik 14-21, 21-19, 21-18 in 63 minutes.
Yuta Watanabe and Arisa Higashino won the mixed doubles title without breaking a sweat.
The third-seeded Japanese took the title with a walkover win over fourth seeds Wang Yilyu and Huang Dongping of China.
Second seeds Nami Matsuyama and Chiharu Shida of Japan were crowned the women’s doubles champions after another walkover win against top seeds Chen Qingchen and Jia Yifan of China.
Wang and Chen reported sick due to diarrhoea and withdrew from their respective matches.