Nirat's 61 bested the old mark of 62, which was set last year by Wen-Chong Liang, then matched later on by Edward Loar.
'I am very happy, I drove well and was bogey free,' said Nirat, who tied for eighth at this year's Indonesia Open.
Raphael Echenique of Argentina is alone in second place at 8-under-par 64.
Keith Horne, Richard Lee and Wen-teh Lu are knotted in third place at minus- 7.
Yalong Bay Golf Club yielded many low scores in round one as 92 players broke par on Thursday. However, no one was within three shots of Nirat, who is not a member of the European Tour.
He opened on the back nine Thursday and wasted little time in breaking into red figures with a birdie at the 10th. Nirat added back-to-back birdies from the 12th, then closed his opening nine with birdies at 16 and 18.
Nirat started his second nine exactly as he started his front, as he birdied No. 1. It's hard to imagine him playing any better than he already was, but Nirat rattled off four consecutive birdies from the fourth to reach 10 under par.
He birdied his final hole, the par-5 ninth to establish the new course record.
Nirat credited past experience as a factor in his amazing round on Thursday.
'I played here last year so I am familiar with the course, which helps,' he said.
Echenique, who is a rookie on the European Tour this year after a seventh-place finish on the Challenge Tour last year, started with birdies at the second and fourth holes.
The 26-year-old closed his front nine with back-to-back birdies at eight and nine. Echenique kept the momentum going with a par from left of the green at 10, then recorded his fifth birdie of the round at the par-4 12th.
At the par-5 13th, Echenique drove into a bunker off the tee, then hit a spectacular second shot from 220 yards to 15 feet. He drained the eagle putt and found himself 7 under par for the championship.
Echenique birdied the 14th and became the first player to get to minus-8. That did not last long as he bogeyed the 240-yard, par-3 15th, but the rookie had one more good hole left.
Echenique birdied the closing hole at Yalong Bay Golf Club to get into the clubhouse at minus-eight.
'The course is beautiful here, but I heard that it was easier last year as there was less rough,' said Echenique. 'But I played really good today. I was driving it perfect and my putting was excellent.'
Lee Westwood, Scott Hend, Wade Ormsby, Carl Suneson and James Kingston share sixth place after opening rounds of 6-under-par 66.
Liang, who defeated Iain Steel in a playoff last week to win the Singapore Masters, shot a 3-under-par 69 on Thursday and is part of a group tied for 37th place.