At, Anaheim, California last night, Prannoy beat Kashyap 21-15, 20-22, 21-12.
Prannoy had found a place in the final after defeating Vietnam's Tien Minh Nguyen, while Kashyap overcame Korean Kwang Hee Heo in the semifinals.
"It was a good match, pretty intense match, a high quality match by both me and Kashyap. I think after losing the second game narrowly, I was calm and patient enough and it worked for me," Prannoy told PTI.
"In second game, Kashyap was playing better than the first game. He was putting a lot of pressure on net and he was also finishing the lifts that I was producing, that made the whole difference.
"But in the third game, I changed my strategy a bit and I had a good lead. So yeah, overall happy with the tournament. Now I am looking forward to New Zealand Open," he added.
The duo, who had a 1-1 head-to-head record having played each other at the 2014 German Open last time, engaged in fast-paced rallies and Prannoy more often sealed the rallies with his powerful smashes.
In the first game, Kashyap moved to a 7-1 lead before entering the interval with a sizzling smash on the forehand of Prannoy, who slowly reduced the gap to 9-12 and then turned the tables with five straight points.
Kashyap clawed back to level par at 15-15 but Prannoy looked unstoppable as he reeled off six straight points to grab the first game with another cross-court smash.
The second game had some intense moments as the duo fought fiercely for each point. The rallies were more aggressive with each having their share of moments.
Kashyap lead 14-9 at one stage but Prannoy drew parity at 15-15. Kashyap continued to exert pressure on his younger colleague and had a 20-18 lead.
Prannoy grabbed two points before Kashyap roared back into contest with another superb smash.
In the decider, Prannoy changed his strategy. His deft touch in the lifts and better net strokes earned him points as he zoomed to a 13-7 lead. The 24-year-old continued to move ahead and eventually seal the issue when Kashyap misjudged a shuttle at the baseline.
Ever since bursting on to the scene with a silver medal at the 2010 Youth Olympics, Prannoy has been often left on the sidelines due to injuries, affecting his training and thereby his progress.
He fought through a knee injury in 2011 and back injury in 2012 to reach the finals at the 2013 Tata Open. A series of semifinals at Bitburger, Syed Modi International, Macau and a final at Vietnam was followed by a maiden Grand Prix Gold win at Indonesia in 2014.
Another injury-marred year followed but he still managed to reach a career-best world ranking of 12. He recovered to win the 2016 Swiss Open but again sustained a toe injury at the Singapore Open and subsequently missed the Thomas Cup.
He was in rampaging form at the Premier Badminton League this year but injuries to his knee and toe once again came back to haunt him.
But he once again regained fitness and reached the semifinals at Indonesia Super Series Premier, stunning Olympic silver and gold medallist -- Malaysia's Lee Chong Wei and China's Chen Long on the way.
"I have been playing well, if the injuries are off then I am okay, I could not play well in Canada, as I had an inflammation in the tailbone area. Probably that did the damage in Canada," he said.
"But I worked on it in the regular training and I am happy I could give my best here. I am not too disappointed with my losses at Australia and Canada as I know its part and parcel of the game."
In the women's singles of the tournament, Japanese Aya Ohori won the final beating Michelle Li of Canada.
It was the second time this season that two Indians fought out for the title at international badminton.
In April, K Srikanth and B Sai Praneeth had played in the finals of Singapore Open with Sai Praneeth claiming his maiden Super Series title....