The 28-year-old Lahiri, buoyed by an automatic selection to the International Team for the President's Cup next month, had five birdies against two bogeys, both of which were three-putts.
Lahiri, who in the morning session was as high as tied third at one stage, was in the end, three shots behind joint leaders, American Tommy Gainey and Argentine Emiliano Grillo, who shot 66 each.
Seven players including Ricky Barnes shot 67 each, while another six carded four-under 68 each on an excellent day for scoring.
"I think I hit it decent but I wasn't very good off the tee. Any other day I would have said driver would be my best club but it would be the 14th club in the bag today. I was all over the place," Lahiri said.
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Lahiri hit some good iron shots but couldn't get the putts to drop. "It was slightly frustrating on the back nine," he said.
This is the first tournament in the Web.Com Tour Finals, a series of four events that will conclude at the Web.Com Tour Championship in Ponte Vedra Beach, Florida. Twenty-five PGA Tour cards are up for grabs during the four Finals events, as well as positioning for all 50 cards, of which 25 were awarded two weeks ago at the end of the regular schedule.
The two blemishes on Lahiri's cards were bogeys on the first and seventh hole, both a result of three-putts after duly getting to the greens in regulation.