Bradley, who also won the Byron Nelson Championship this year, finished the playoff at 1-under par, besting Dufner by a single stroke at the Atlanta Athletic Club.
The 25-year-old became just the third golfer in PGA history to win in his first appearance in a major championship. The others were Francis Ouimet at the 1913 U.S. Open and Ben Curtis at the 2003 British Open.
He also became the first American to win a major since Phil Mickelson took last year's Masters -- a six-tournament span that was the longest drought for the United States in PGA history.
2014: The Year in Music [PHOTOS]