Siddikur, 29, had five birdies and a lone bogey for a three-day total of 12-under-par 204 after the penultimate round in the $300,000 event at the Delhi Golf Club.
"I'm so happy," said a smiling Siddikur, who is chasing his second Asian Tour title. "I've been very consistent. I'm happy with myself with three 68s.
"I've been trying to get more regulation play and it's been working. Conditions are not easy. It's not finished until the last hole and last putt.
"This course is never easy but I'm looking forward to playing with Anirban as he's a good friend of mine."
The 25-year-old Lahiri, who started the day four shots off the lead, charged ahead with some strong hitting for a blemish-free round of six-under 66.
The defending champion, seeking his third Tour win, got back in contention with birdies on the last two holes.
"It's the best I have played all week. I'm getting more comfortable on the greens. Just a couple of bad swings but I got away with pars which was important," Lahiri said.
"Four putts kind of stood at the lip but I'm not going to complain as some fell for me in the end. I'm happy with where I am right now."
Joint overnight leader Khalin Joshi struggled to a one-under-par 71 to lie two strokes back while another local hope, Rashid Khan, was a further shot behind in fourth.
The other overnight leader, American Chan Kim, stumbled to a two-over-par 74 to finish five shots behind the leader and tied for seventh.
204 - Siddikur (BAN) 68-68-68.
205 - Anirban Lahiri (IND) 71-68-66.
206 - Khalin Joshi (IND) 66-69-71.
207 - Rashid Khan (IND) 72-64-71.
208 - Chapchai Nirat (THA) 66-75-67, Shiv Kapur (IND) 69-70-69.
209 - Matthew Stieger (AUS) 70-71-68, Chan Kim (USA) 67-68-74.
210 - Pawin Ingkhapradit (THA) 70-69-71.