The 24-year-old Indian, chasing his second Asian Tour title within the space of a month, battled to a three-under-par 68 at the Macau Golf and Country Club to lead the popular Asian Tour event on 11-under-par 131.
Thitiphun, 20, fired an impressive 66 to jump into tied second place with countryman Prom, who produced two chip-in birdies in his round of 68.
Filipino star Angelo Que (66), Thai ace Thongchai Jaidee (68), Bangladeshi Siddikur (68), Brazilian Adilson Da Silva (66) and Australia's Kieran Pratt (68) are a further shot back on 134 in the event which is title sponsored for the first time by The Venetian Macao-Resort-Hotel.
After an opening round of 63, overnight leader Bhullar was somewhat more subdued with four birdies against an opening bogey today [Friday]. He took 29 putts over the tricky Macau layout but extended his recent good form which has yielded two top-10s and a win at the Yeangder Tournament Players Championship in Taipei.
"Not as good as yesterday [Thursday] but considering the conditions right now, it's not a bad score," said Bhullar. "I could have done much better but there is a lot of golf left. Hit the ball good but had some bad luck ... had two or three lip outs."
Bhullar, ranked sixth on the Order of Merit, was delighted to maintain his dominance in Macau as he chases a fourth Asian Tour title. "It always feels good to play in the leader group week after week. It proves the standard of golf is improving. I'm looking forward to playing in the weekend. I'm just going to stick to my routine and process and see what happens," he said.
Thitiphun, one of many emerging young Thais, scrambled well to keep the bogeys off his card. "I missed a few shots but I got up and down on three occasions. Bogey free around here, I'm happy," said the bubbly Thai, who turned professional when he was 16.
The youngster reckons he will be nervous over the weekend but is hopeful he can sustain his title push. "Last year was my first time on Tour and I think I have learned from my experience. Mentally, I'm better now. I'll be a bit nervous tomorrow [Saturday], seeing names like Thongchai Jaidee and Gaganjeet Bhullar. But I feel I have a chance."
The burly Prom stayed in touch with Bhullar, thanks to some hot iron play which produced two chip-in birdies on 11 and 18. "I struggled, especially with my putting in the first five holes. But I got it back, had a good finish on the back nine with a two under. My driving wasn't good and I didn't have the confidence. I'll need to fix it at the range," said Prom, who is seventh on the Merit list.
Que, a three-time Asian Tour winner, showed he did not require a practice round to chart his way up the leaderboard with an eagle and six birdies on the card. "I've played this course since 2003 and it's pretty much the same course every year. If you're confident with your game, you can manage your game around here," said Que, who came home in 30.
"I was hitting good shots but I didn't get lucky and wasn't holing any putts early on. It was a straight forward eagle (on two) from 15 feet but it jump-started my back nine and I had four more birdies after that."
Chinese legend Zhang Lian-wei, a two-time Macau Open champion, maintained his proud record of making every cut since 1998 with a 72 leaving him on 141, the same score as title holder Chan Yih-shin of Chinese Taipei, who fired a 68.
Veteran Welshman Ian Woosnam, a former Masters Tournament winner, carded a 72 to lie on 140. The halfway cut was set at 143 with 76 players progressing into the final two rounds.