Atwal managed two birdies against two bogeys and a double bogey to be two-over for the day and end the tournament with a total of three-over 291.
The Orlando-based golfer was one-over in the front nine after managing to sandwich a birdie in between a couple of bogeys.
The back nine comprised a double bogey against a birdie as Atwal rounded off his campaign on a rather disappointing note.
Italian Francesco Molinari clinched the title by a stroke after a second successive 67 left his overall score at 19-under 269.
England's Lee Westwood finished second after returning a 67 in the final round.