"This game kicks you more often than it gives you a pat on the back," McDowell said. "It's hard to win."
Not on this day for McDowell, who pushed forward on wind-blown Harbour Golf Links when his rivals were moving backward, unnerved by the 20-30 mph winds that rattled the course.
He rallied from four strokes down when the day began to take a one-shot lead into the 72nd hole. Then after he made his only bogey of the round to fall into tie with Simpson, two-putted from about 15 feet to make a par on the extra hole that Simpson couldn't match.
"I guess the weather was what the doctor ordered. I needed that to get close to the leaders," said McDowell, who earned $1,044,000 for the victory.
McDowell, from Northern Ireland, had a 69, one of only three scores in the 60s among the 70 who teed off Sunday.
Simpson, reigning U.S. Open winner, shot 71. He had a chance to win in regulation, but his 22-footer for birdie went 3 feet past and set up the additional hole. "I came in with not too much confidence, but I just stayed true to the process of what we've been working on," Simpson said.
Bernhard Langer added to his impressive Champions Tour season by shooting a 67 to win the inaugural Greater Gwinnett Championship by three strokes in Duluth, Ga.
The 55-year-old Langer, who finished 10 under, took control with a long chip-in for birdie on No. 10. He had six birdies for his fifth top-three finish in six events. Tom Lehman, whose 67 included birdies on 17 and 18, tied for second at 7 under with Tom Pernice Jr.
*-Graeme McDowell -9
Webb Simpson -9
Luke Donald -7
Kevin Streelman -7
Jerry Kelly -6*- won playoff