The Bangalorean who turns 20 next month was leading by a solitary shot from Vashista Pawar.
Another local lad Udayan Mane shot a 1-under par 71 to be tied for the third place along with Nikhil Sekhawat and Aman Raj.
As many as six players - Ainesh Ahluwalia, Arjun Singh, Vikram Rana, Advait Luthra, Samarth Dwivedi and Ankur Chadha shared the sixth place at 72.
Trishul who regularly plays at KGA began in the right earnest making a birdie on the opening hole.
With consecutive birdies on the fourth and fifth, he was on a roll.
However, a double on the tough par-4 seventh, owing to a mistimed shot from the green side bunker, pulled him back a bit.
He regained two shots, making back to back birdies on the eighth and the ninth to take the turn at 3-under.
Although he missed on a couple of birdie opportunities from short distance, Trishul ensured that he did not commit any mistakes as he parred his way on the back nine to remain status quo.
"My hitting was a bit awry but I am happy with my round," said Trishul who hit 14 greens in regulations.
"I am looking to build up on the lead and take home the trophy," added Trishul whose best finish this season has been a 5th place in the Tata Steel Northern India Amateur.
Meanwhile Coimbatore lad Vashista Pawar made five birdies but yet returned a card of two-under 70. His birdies came on the 4th, 5th, 7th, 8th and 14th while making bogeys on the 12th, 13th and 17th.
Top scores (after 18 holes)
69 Trishul Chinnappa; 70 Vashista Pawar; 71 Udayan Mane, Nikhil S Sekhawat, Aman Raj; 72 Ainesh Ahluwalia, Arjun Singh, Vikram Rana, Advait Luthra, Samarth Dwivedi, Ankur Chadha; 73 Hemendra Chaudhary, Piyush Sangwan, Pukhraj Singh Gill
--IBNS (Posted on 03-09-2013)