Lahiri, starting the day at 10-under, is now only five-under and trailing new leader, Australian Cameron Smith (71) by three shots.
Smith snatched a one-shot lead from Thai duo Chapchai Nirat and Sattaya Supupramai.
Other Indians -- SSP Chowrasia (73) is now tied eighth, Jyoti Randhawa (73) and Chiragh Kumar (69) are tied 23rd, while Rashid Khan (72) is tied 38th. Arjun Atwal (79) slipped to 71st.
Lahiri, who came down with a stomach bug, staggered home with two birdies against three bogeys and two double bogeys.
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"I took some medication before the round but at the seventh, it got too much and I had to go (to the restroom). Every 20 to 30 minutes, I kept getting spasms. It was tough. But having said all that, I should have done better than I did. I'm still only three back though. I have to play as I did in the first day and try to get into the zone and make as many birdies as I can (tomorrow)," he said.
Chapchai shot a 69, while Sattaya moved into contention with a 68 that included six birdies and two dropped shots over his last three holes.
Current Order of Merit leader David Lipsky of the United States kept himself in the hunt for a second title in three weeks with a battling 69 which left him two back alongside Australian Jake Higginbottom and Chinese Taipei's Hung Chien-yao.