Lahiri, who has won three Asian Tour titles at home and all on the Delhi Golf Club, carded a second straight four-under 67 to move to eight-under 205 and in fourth place.
Lahiri is three shots behind the leader, Bangladesh's Siddikur (67), who was at 11-under with rounds of 66, 69 and 67.
Rahil Gangjee, the only other Indian to make the cut, carded 70 and was lying 30th at one-over 214. Gangjee started with a double bogey and then had three birdies on second, sixth and eighth.
"I'm happy that I've found my rhythm. I'm playing well and hitting the ball good. It's my first week back with my short putter and that's a very big positive for me," said Lahiri.
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"I've been coming here for the last five years and I'm starting to feel very comfortable here. I've learnt how to navigate this tough course," added the Indian.
Despite the overwhelming support for home favourites at the Santiburi Samui Country Club, the 28-year-old Bangladeshi stamped his authority by taking a slender one-shot lead over Thailand's Prayad Marksaeng with his three-day total of 11-under-par 202.
Arnond Vongvanij of Thailand signed for a 68 to take the third place while Lahiri stayed on course taking the fourth place with a 67.