Lahiri birdied his last regulation hole from 10 feet to tie Rashid Khan at 15-under-par 273 and sank a four-foot birdie on the same hole to clinch his third Asian Tour title, all three coming via playoffs and at the DGC.
Lahiri's love affair with the par-72 course began in 2011 when he triumphed in a three-way playoff to win the Panasonic Open before returning to pip Prom Meesawat of Thailand in the playoff in last year's SAIL-SBI Open.
"I'm still in disbelief that I made the putt in regulation and got into the playoff," said 25-year-old Lahiri who signed a final round of four-under-par 68.
"After that, in the next 15 minutes, I didn't know what happened. Unfortunately for Rashid, it didn't work out. I feel bad for him as he doesn't have a card on the Asian Tour.
"Once I got into the playoff I felt I had the upper hand ... I've played the 18th hole I don't know how many times now, probably 24 times, three extra times. It's been nice to me," he added.
Khan did not hide his disappointment after falling short of his maiden Asian Tour title despite a final round of six-under-par 66.
"Starting with a par on the first day and losing in a play-off, it's disappointing," said the 22-year-old who virtually grew up at the DGC.
Overnight leader Siddikur Rahman of Bangladesh was not in control of his shots and went one-over-par 73 to finish four strokes behind.
Local favourite Shiv Kapur was further one shot behind after signing off with a two-under-par 70.
Thailand's Pawin Ingkhapradit and Australian rookie Matthew Stieger ended in tied fifth place.