The victory vaulted Donald back to the No. 1 spot in the World Golf Ranking.
Donald made his birdie putt after Jim Furyk and Sang-Moon Bae missed long birdie trys and Robert Garrigus missed an 8-footer.
Donald replaces Rory McIlroy at No. 1 in the World Golf Ranking. McIlroy had taken over the top spot from Donald when he won the Honda Classic two weeks ago.
Donald closed with 66, Garrigus had 64, Bae had 68 and Furyk had 69.
Ernie Els missed a short par putt on the 18th green to miss out on the playoff.