Lahiri, who went bogey-free for a stretch of 31 holes, began the day on a high after recording three birdies on the front nine.
He sunk his fourth birdie at the 11th to break into the top five on the leaderboard before his round took a turn for the worst.
Lahiri's back nine woe began when he missed a two-foot par putt at the 13th before adding another bogey at the 14th. His putting woes continued on the 17th when he missed a four-foot par putt.
"I hit the ball well to about 25-30 feet for a realistic birdie on 13th and then three-putted," he told reporters. "I played just one hole badly, the 14th. When you hit the trap you take a bogey. I played alright. Just that you shoot yourself in the foot when it comes to scoring.
"I just missed one green and needed 35 putts. I three-putted on the par-5 fifth (got a par), then 13th and 17th, where I had bogeys."
Lahiri was also at a loss of words to explain his dismal putting, especially at the 13th and 17th hole, where he should have recorded pars.
"I had nine putts on the last four. I hit the ball well, to 12 feet on 15th, 15 feet on 16th and then 30 feet on the 17th. On the 18th I hit to 20 feet," he said. "The 13th to 17th is the toughest stretch on this course. It’s the hardest every day. Look at what I’ve done – I haven’t hit an OB, not hit in the rough.
"My game is right up there. So I’m extremely disappointed. I just need to get the confidence back on the greens. Nothing major, just a tweak and it should be fine."
Lahiri finished with a one-under par 71 and currently sits in a tie for 26th. But, the 28-year-old believes that he wouldn't be trailing leaders Paul Dunne, Louis Oosthuizen and Jason Day by six strokes if he hadn't faltered on the back nine.
"I should have been in the 60s today," he said. "I’m enjoying myself and playing well. The course suits my eye. I need to play happy golf and avoid silly mistakes like I did when I missed a two-footer.
"I’m playing well to make 4-5 birdies and will be trying to keep my sheet clean like I did in the second round."