South Korea's Sungjae Im claimed his first PGA Tour title in the Honda Classic as overnight leader Tommy Fleetwood had to settle for a tie for third place.
Im carded a closing 66 at PGA National to finish six under par and a shot ahead of Canada's Mackenzie Hughes, with Fleetwood another stroke back following a final round of 71.
Fleetwood took a one-shot lead into the final round and stretched his lead to three with birdies at the first and second, only to drop shots on the sixth, eighth and 13th to fall two strokes behind.
A birdie from 25 feet on the daunting par-three 17th meant Fleetwood needed another on the par-five 18th to force a play-off, but the Ryder Cup star pushed his approach into the water to the right of the green as a spectator appeared to scream "get in the hole" at the top of his backswing.
Ireland's Shane Lowry carded a final round of 70 to finish in a tie for 21st.
"You live or die by the shots you hit," Fleetwood told Sky Sports. "I had a chance on the last. The swing wasn't there all day and I had a few iffy shots in me.
"I didn't get anything out of the round until 17. It was such a great moment, I felt great walking to the last and hit a great tee shot.
"It was a hard number (for the second shot), I had to hit a massive cut with a five wood and came out of it and that was that. It's golf, I'm upset but I'm fine.
"I had a stretch today where not a lot happened but feel like I'm doing a good job of staying there, I'm getting there more and more often and yeah I'm not winning them all, but coming down the last hole I've been there every time and it's just not happened."
Im began the day three shots behind Fleetwood but birdied four of the first five holes before dropping a shot on the seventh.
A birdie on the 11th was followed by back-to-back bogeys but the 21-year-old responded superbly to birdie the 15th and 17th and crucially saved par from a greenside bunker on the last.
"I've been in this spot many times and just gaining the experience throughout the weeks and that really helped me stay in the moment," Im told NBC through an interpreter.
"Those experiences really helped, especially coming down the last few holes and I pulled out the win.
"I knew I was one back going into the last four and just wanted to get a little bit more aggressive rather than be tentative on those holes. I was hitting the ball really good and felt that I could get at those pins."