Phadungsil had seven consecutive birdies over Nos. 10-16 and finished the first round at 11-under 61 after a 28 on the back nine at the Jaypee Greens Golf Club.
He's five strokes up on Magnus Carlsson, Abhijit Singh Chadha, Liang Wen-Chong, Chapchai Nirat and Chawalit Plaphol, who turned in scores of 6-under 66.
Chadha and Liang didn't have a bogey in their rounds. Carlson and Nirat each had an eagle, five birdies and one bogey while Plaphol's round included an eagle, six birdies and two bogeys.
Eight players are tied for seventh at 5-under 67.
Phadungsil had three birdies in a four-hole span on the front side before his second-nine onslaught.
He had four birdies over Nos. 10-13 before dropping a 50-foot putt for birdie at 14. He nearly pitched in for eagle at the par-5 15th and tucked his approach within 2 feet of the hole at 16. After a par at No. 17, his second shot at the par-4 closing hole stopped 6 inches from the hole for a tap-in birdie.