Lahiri, who carded 65 on first day, added a five-under-par 67 after the second round. The five-time Asian Tour winner compiled a two-day total of 12-under-par 132 to extend his morning advantage over Australia's Andrew Dodt by two shots at the Singha Park Khon Kaen Golf Club.
Chowrasia, who also carded 65 on first day, managed only 71 with just one birdie and no other birdies or bogeys.
Promising Indian youngster S Chikkarangappa, who sees Lahiri as his mentor, shot 68 to move into top-10 in 10th place at seven-under.
Arjun Atwal, 72 on first day, added a 67 today to be five-under and tied 26th, while Rashid Khan, two-time winner this year, carded 69 to move to four-under after 36 holes and is now tied 36th. Of the other Indians Rahil Gangjee (71-71) was tied 64th, Chiragh (72-75) was 103rd and Himmat (75-74) was 127th.