The 51-year-old Victorian closed with a six-under 66 for a four-stroke victory.
Allan finished at 18-under 198 at En-Joie Golf Course at Enditcott, New York for his second win on the 50-and-over tour this season following his breakthrough at the Galleri Classic in California in March.
He opened the tournament with a blistering 63 on Friday for a two-shot edge and had a 69 on Saturday to take a one-stroke lead over Boo Weekley into the final round.
After playing the first seven holes Sunday in one under with two birdies and a bogey, Allan birdied five of the next six and parred the last five.
"It was tough. It was tough, even yesterday, hanging in there, and today early on it was a bit rough with the driver," Allan said. "In the rough a lot and just managed to hang in there. Then on the back nine, made a few putts."
Jason Caron was second after a 68. Weekley (70) and Notah Begay III (67) tied for third at 13 under.
Australia's Michael Wright shot a closing 67 to tie for fifth with Soren Kjeldsen (64) and Jeff Sluman (68).
Padraig Harrington wasn't back to try to win for a fourth straight time, skipping the event to play in the Scottish Open. He also has the British Open at Royal Portrush and the Senior British Open at Royal Porthcawl.
Ernie Els, in the British Open field, shot 69 to tie for 16th at 8 under.
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