The Indian displayed sublime skills to defeat his higher ranked opponent 21-9, 21-14 in 39 minutes at the Wembley Arena and topped Group D.
With the win, Kashyap equalled his head-to-head record against Nguyen to 3-3. Prior to the match, he had not beaten the Vietnamese since June 2010.
The first game started with a neck-and-neck fight as neither player could hold serve as the score read 6-5 in favour of Kashyap.
The 25-year-old Indian found legs and started extending his lead with the help of some exquisite drop shots and in no time went ahead 16-7. Aided by some good smashes, he gained an 11-point advantage at 20-9 before sealing the game.
In the second game, Nguyen put up a better show early on as the scoreboard read 7-7.
Like in the first game, Kashyap with his fast court movement and effective smashes started dominating the World No.11 and took a lead of 18-12 from where there was no looking back and won the game in 19 minutes.
Throughout the match, the World No.21 was impressive at the net and steady from the back, hitting a mix of shots which befuddled his Vietnamese opponent.
The Indian will next face Group C topper Sri Lankan Niluka Karunaratne, whom Kashyap had beaten in Stockholm earlier this year in their only encounter.