The overnight leader needed a birdie at the par-five 18th to force a play-off with Sunghae Im but hit his second shot in the water as he closed with a bogey.

"You live or die by the shots you hit," said the world number 12.

South Korean Im, 21, shot a four-under 66 to win a first PGA Tour title on six under, one ahead of Mackenzie Hughes.

Fleetwood, a five-time winner on the European Tour, took a one-shot lead into the final round at PGA National in Palm Beach, Florida, and he extended that advantage with birdies on the opening two holes.

But in breezy conditions, two dropped shots saw him fall back into a share of the lead heading into the back nine.

A bogey at the 13th then had him playing catch-up as Im produced some stellar golf. The South Korean birdied the 15th and 17th - two of the three holes on the course's famous Bear Trap - and set the clubhouse target.

Fleetwood had to birdie the last two holes to catch him and he holed a putt for birdie at the 17th.

But after a perfect drive down the last, his hopes disappeared when his five-wood approach shot landed in the water.

"That's golf. Of course, I'm frustrated, upset, but I'm fine," he told Sky Sports after claiming a fourth top-three result in his last six tournaments..

"I feel like I'm quite a consistent player. I got up there and had a chance of winning. I'm not doing that as much as I would like, but winning is hard.

"You have to keep pushing forward and I'm not getting worse at golf. I'm getting better."

Lee Westwood shot a level-par 70 to finish joint fourth on three under, while fellow Englishman Luke Donald was two shots further back after closing with a 72.