In doing so, he gets to share the first round lead with Indian rookie Khalin Joshi in the tournament presented by Incredible India, Ministry of Tourism on Wednesday
Chapchai, nicknamed "King Kong" due to his big-hitting game, fired eight birdies against two bogeys at the demanding Delhi Golf Club while the 20-year-old Joshi raised local cheers with a magnificent professional debut on the Asian Tour with nine birdies on the card.
The leading duo hold a one-shot lead from Qualifying School winner Chan Kim of the United States while a further stroke back are India's Chiragh Kumar and Bangladeshi ace Siddikur, who signed for 68s in the US$300,000 tournament.
Home hero Shiv Kapur, chasing a first victory on his home course, produced a magical outward 29 but came home in 40 after taking a quadruple bogey eight on the sixth hole to settle for a 69, three shots from the lead.
The 29-year-old Chapchai is chasing his fourth Asian Tour victory, his last being the SAIL-SBI Open in 2009 when he set a new world record for 72-holes with his winning 32-under-par 256 total.
"My putting was very good. I made a lot of one putts, probably took 27 or 28 putts," said Chapchai, who played alongside Kapur. "Shiv played well on our front nine (on the back) and then I played well coming in. I stuck to my game plan. It's a tough course as the fairways are narrow. But if you hit fairways, you can make birdies."
The powerful Thai was disappointed he dropped bogeys via three putts on the 10th and ninth holes but believes his new putting routine is pushing him towards a return to the winner's enclosure. "I started on 10 with a three putt and finished at nine with a three putt, so that was not so good. But the putting was still pretty good overall. I stuck to my new putting routine and didn't take too much time over my putts. I feel confident," said Chapchai.
After ending 2012 as India's number one amateur, Joshi took the plunge into the play-for-pay ranks and won the PGTI's qualifying school. He missed his card at the Asian Tour Qualifying School in January but victory on Saturday will certainly fast-track his career.
"It will mean the world to me if I can win my first Asian Tour tournament as a pro. I'm looking forward to it," said Joshi, who hails from Bangalore and looks up to title holder Anirban Lahiri who is also from Bangalore.
The slender Indian produced a blazing finish, nearly shooting a hole-in-one on his 16th hole of the day at the seventh and missing an eagle chance from 12 feet at the next hole. He then slid a 10-foot birdie attempt past the cup for the outright lead.
"I've been hitting the ball well the past few weeks but the putter was hot, made quite a few. I'm going to approach the rest of the week like how I did today [Wednesday], just play within myself. Anirban is a great friend of mine and I look up to him. I'm looking forward to doing something this week. Indeed, this is my best round at the DGC. It was very nice."
Chan produced two sensational chip-in birdies on the sixth and nine holes as he moved into contention in his rookie season on the Asian Tour, which is celebrating its milestone 10th season in 2013.
"My playing partners in Myanmar (two weeks ago) were telling me how narrow it was here and I looked on-line and it didn't look as narrow. But when I stepped on the first tee on Monday, I kind of got a taste of how it really is," he smiled.
"You have to be smart off the tee. The longer clubs you hit, you have to be really accurate. I think I hit three three woods and the rest were hybrids or irons off the tee. You can't be too aggressive but it's definitely scorable."
The main sponsors of the SAIL-SBI Open, which is celebrating its sixth edition, are the Steel Authority of India Ltd, State Bank of India Ltd and Incredible India, Ministry of Tourism.