It also brought Lahiri an early wedding gift, as he is getting married next month.
Lahiri, who started the day in second place and began well by firing three successive birdies starting from the second hole.
He seemed to have been affected by a break prompted because of a three-hour rain stoppage, as he double bogeyed 13th when play resumed.
Lahiri (68) finished at 17-under after rounds of 70, 69, 64 and 68 and was one shot clear of Baek (65) and Cameron Smith (70).
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"I had an awkward lie on 13. During the rain delay I was just thinking that I have to get up and down there. I got a bad break there but I knew Lin Wen-tang dropped a shot as well. Unfortunately I got a double bogey there but I am glad I came back strong," said Lahiri.
On his final step, Lahiri said, "My mind was blank when I prepared for the last putt on 18. All I told myself was I had to get it into the hole. When I was walking up to the greens, I was actually thinking if I need to prepare for a playoff tomorrow morning."
Lahiri let out a scream of relief as the ball settled inside the cup.