Home favourite Chowrasia, whose only previous European Tour win also came on Indian soil, looked to be cruising to victory as he notched up seven birdies to reach 17 under at DLF Golf and Country Club.
But he snatched at his tee shot on the par three 16th, pulling his six iron way left and double bogeying to be 15 under with two to play.
Englishman Coles has never been better than third on The European Tour, but a birdie at the 18th gave him a one shot lead when the third round was completed early on Sunday after five hours of fog delays over the first three days.
And the 38 year old steadily progressed to three under through 12 holes to sit level at the top of the leaderboard.
Third on the leaderboard was US Open Championship runner-up Grégory Havret, but three back on 12 under and with only one to play he was unlikely to be taking home the €300,000 first prize.
With seven holes left to play, Indian golfing legend Jeev Milkha Singh still had time to mount a challenge from 11 under. He was level with first round leader Robert-Jan Derksen, Thai Chinnarat Phadungsil and another Indian, Sujjit Singh.
Chowrasia’s birdie putt at the last stayed above ground, so Coles needed to play the last four in one under to take the title.