Thailand's Phadungsil carded a sparkling 28 during his inward nine at Jaypee Greens Golf Club to distance himself from Abhijit Singh Chadha, Chapchai Nirat, Magnus A. Carlsson, Wen-Chong Liang and Chawalit Plaphol, who all shot 66.
"That's my best ever round," said Phadungsil. "Today I had a lot of great putts."
David Drysdale, Scott Hend, Scott Barr, Rikard Karlberg, Thomas Aiken, Jaakko Makitalo, Rashid Khan and Joonas Granberg are knotted in seventh place after opening round 67s, while two-time champion S.S.P. Chowrasia highlights a large group knotted in 15th at minus-4.
Thailand's Thongchai Jaidee, the highest ranked player in the field at world No. 59, recorded a 2-under 70 during an up-and-down round which included an eagle, four birdies, a pair of bogeys and a double bogey.
Defending champion Jbe Kruger, who earned his first European Tour win at this event a year ago, shot even-par.
Chadha, an Indian Tour regular, got off to a strong start on his home soil.
Making his first European Tour start, the 21-year-old carded six birdies during his bogey-free opening round. Beginning on the back nine, he picked up shots on Nos. 15 and 16, executed a hat trick of birdies starting at the fourth, and capped his round with another birdie on the ninth.
"I've got no experience at all," admitted Chadha. "I've played a couple of events on the Asian Tour, and playing with the big boys really gives you lots of confidence and it's a really good feeling for me."
Chadha's effort was enough to vault him to the top of the leaderboard, but the advantage proved fleeting given Phadungsil's assault on Jaypee Greens.
The 24-year-old's round began ordinarily enough, with six pars and three birdies during an outward 33, but the closing flurry proved spectacular.
Phadungsil opened his inward stretch with four straight birdies, then kept the run going with a 50-foot birdie roll on the 14th. After nearly pitching in for eagle on the 15th, the former European Tour Qualifying School graduate picked up another shot at the 16th to cap the remarkable seven-birdie flurry.
After parring the 17th, Phadungsil dropped an iron within six feet at the last and tapped in for his eighth birdie of the back nine and a commanding advantage.
"Back nine I hit the driver better than the front nine. But I holed my putts -- that's why I made my score," said Phadungsil, who has three Asian Tour titles to his name. "Today my game was very good so I will keep going."
NOTES: Chowrasia won this event in 2008 and 2011 ... Vinod Kumar withdrew on Thursday ... The tournament is being held at Jaypee Greens Golf Club for the first time. DLF Golf & Country Club staged the event the previous three years ... This event is tri-sanctioned between the European Tour, the Asian Tour and Professional Golf Tour of India ... Last year, Kruger fired weekend rounds of 66 and 69 to win by two strokes over Marcel Siem and Jorge Campillo. Kruger ended the event at 14-under-par 274.