Europe took a three-point advantage into a weather-delayed final day at Celtic Manor, where Colin Montgomerie faced an American fightback on the Monday.
The two sides were locked at 13.5-13.5 with the final match still on the course, leaving the Americans needing a half-point to retain the trophy and McDowell requiring a victory to win the trophy for Europe.
Hunter Mahan was three down after 11 holes but bounced back within one with three holes to play, only for McDowell to drain a timely putt at the 16th to give the Northern Irishman control of the contest.
McDowell went on to take the match 3&1 to complete a 14.5-13.5 win for the hosts and the first of three consecutive European Ryder Cup victories.
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