The fact it happened for a Scot playing at St. Andrews, the home of golf, made it more satisfying.
Gallacher rolled in a four-foot putt to win after McDowell hit his second shot into the Swilcan Burn, the stream that runs across in front of the green on the first hole of the Old Course.
The victory in his 188th European Tour event earned Gallacher US$800,000 after two second place finishes. McDowell won US$533,330.
Gallacher, nephew of former Ryder Cup captain Bernard Gallacher, shot a five-under-par 67 in the final round. McDowell, who fired a course record-equalling 62 in the first round, carded a 68.
They totaled 269, 19 under par, to finish a shot clear of European Ryder Cup players Ian Poulter and Luke Donald. Poulter closed with a 69 while Donald, who led overnight, could only manage a 71 after leaving a 15-footer for birdie at the last just short to miss out on the playoff.
They both won US$270,200 in one of the richest events in Europe.
Defending champion Lee Westwood closed with a 67 to take a share of fifth place with David Howell, who had 71 after a double bogey at the Road Hole 17th.
Ernie Els and Fred Couples shared seventh place, world No. 2 Els shooting a 70 after a first-hole bogey when he went into the Burn, and Couples a 69.
World No. 1 Vijay Singh could only manage 70 and finished sharing 18th place.
RSS