The 25-year-old sits 11 under-par, followed by five players on six-under: Thais Chapchai Nirat and Chawalit Plaphol, India’s Abhijit Chadha, China’s Liang Wen-chong and Sweden’s Magnus Carlsson.
Briton David Drysdale was among eight golfers a shot back from them with compatriots Oliver Fisher, Tommy Fleetwood and Matthew Baldwin among 15 others trailing those by a further stroke.
Chinnarat was only one shot away from equalling the Asian Tour’s record. The tournament at the Jaypee Greens Golf Course is tri-sanctioned by the Asian Tour, European Tour and Professional Golf Tour of India.
He reached the turn in 33 after three birdies before leaving his rivals behind with a back-nine 28.
“It’s my best-ever round," he said. “On the front nine I was hitting a lot of hook shots, so my putter really saved me.
"But on the back nine, I drove the ball better and my irons were also better, so that’s the reason why I scored so well."
Local hope Chadha, 21, was the clubhouse leader in the morning.
“I like this golf course as it suits my game," he said after shooting six birdies and no bogeys.
“I don’t feel the pressure of playing in the Avantha Masters for the first time. The experience of playing many big international events during my amateur days has really helped me."