Lahiri fired six birdies through the last 13 holes after scoring a birdie, bogey and double bogey in the first four on the final day here.
Lahiri, who had a five-under 65 on second day and 66 on final day also had 72 and 71 on first and third days. It saw him aggregate six-under 274 and ended Tied-46th. It was a fair improvement of T-68 at the end of 54 holes.
Sergio Garcia made a par on the first playoff hole to beat Brooks Koepka for his ninth career PGA TOUR victory.
The 36-year-old Spaniard overcame four bogeys, and two balls in the water on the back nine, for a 2-under 68 to get to 15-under 265. He was two groups ahead of the final pairing of Jordan Spieth and Brooks Koepka, who bogeyed the 14th and 15th holes and just missed a birdie chance at 18.
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He admitted that he did miss some putts, saying, "I missed a bunch of makeable putts today, but I am happy with the game and hopefully I will see more of this next week."
On the fourth, he said, "I had a bad drive and it led to a bad hole. I also missed a 10 footer for bogey."
With another win at the Byron Nelson, Garcia matched Seve Ballesteros for the most PGA TOUR victories by a Spanish-born player.
Koepka, who started the day with a two-stroke lead over Spieth, was 17 under after his last birdies of the day, at Nos. 7 and 9. He shot 71.
Matt Kuchar was a stroke out of the playoff at 14 under after a 65.
World No. 2 Spieth had two bogeys in his first five holes yesterday and went on to shoot 74. He finished tied for 18th at 10 under.
He bounced back bravely with a birdie on four and an eagle on five, but with his putter going cold on the homestretch, Thomas ran away with the tournament.
Crestfallen Lahiri admitted, "Disappointment obviously. It was obviously a harder start. I got unlucky with the tee shot and just compounded my errors. My short game again, coming up a little bit to bite me. I tried my best. I fought back as best I could, but I just couldn't get the putts to fall on the back nine.
With his game going up by several notches over the last year, Lahiri knows his time will come, but added, "I have the confidence. It's not like I need additional confidence. But I need validation now. I need validation in terms of my game. I need to see that happen. It's just not happened enough, and it's been a year of near misses so far."
Speaking of Lahiri's misfortune, he said, "That was just unfortunate, it really was. You never want something like that to happen. That's one of the things that happens when you win, you get a little luckier breaks. You get fortunate. Anirban, he really played well. He hit some really good putts that didn't go in, and there's nothing for him to be down or upset about.