Lahiri, a three-time winner on Asian Tour, and Khan, who achieved his breakthrough win only last month in India, shot the day's best of eight-under 64 each and zoomed to 13-under and 12-under respectively, while Smith (67) was at 14-under.
Adding cheer to the Indian camp were SSP Chowrasia (69) at 10-under and Jyoti Randhawa (67) at nine-under were tied fifth and tied seventh, as four Indians figured in top-seven. Rahil Gangjee (72) was tied 24th and Arjun Atwal (73) was tied 50th.
Smith, who has enjoyed a distinguished amateur career, compiled a three-day total of 14-under-par 202 to head into the final round in pole position in what is only his second professional event on the Asian Tour.
Lahiri, playing flawless golf, showed why he is marked out as India's best and one of the most impressive youngsters in Asia, as he fired eight birdies against no bogeys and moved from five-under to 13-under.
At one point after four birdies in a row from ninth to 12th, he was actually in lead, before Smith moved in. He had two birdies on 13th and 14th and a bogey on 15th but was still tied with the Indian at the 18th tee before another birdie saw him pull ahead.
Lahiri, who played a key role in Team Asia's epic 10-10 draw with Team Europe at the EurAsia Cup last month, continued to impress when he got off the starting tee quickly with birdies on holes two, five, six and nine for an outward 32.
He further asserted himself with three successive birdies starting from the par-four 10th and would complete a sensational round by closing with another birdie on 18.
