Davies, the 2004 champion, shot a final-round 5-under 68 to go with a 67 on Saturday for a one-stroke victory over Spains Tania Elosegui at Metropolitan Golf Club.
The 45-year-old Davies finished with a 7-under total of 285. Davies bogeyed the 18th hole while Elosegui birdied 17, putting the Spanish player into the lead with one hole to go and Davies in the clubhouse.
But Elosegui (70) had a double bogey-6 on the 18th to give Davies the title. Australias Karrie Webb was tied for sixth after a 74, five strokes back.
Davies won her 29th career Ladies European Tour title and also has 20 victories on the LPGA, including five majors.
In these conditions, youve just got to take what you can get, Davies said. I had a stupid three-putt (for bogey on the par-3 11th), but overall I played well, played solid.
Another English golfer, Melissa Reid, was tied for third after a 69 Sunday, level with South Koreans Choi He-yong (69) and Lee Chang-hee (73). Lee led after each of the second and third rounds and took a one-stroke lead into Sunday.
Australian Katherine Hull (70), who won last weeks Australian Masters, finished tied for sixth with Webb.
Two Americans who trailed Lee by one stroke into the final round faded badly. Former star amateur Alison Walshe was tied for 16th after a 78 and Beth Allen was tied for 26th after an 80.
The top American was Diana DAlessio, who tied for 13th after a 75, seven strokes behind Davies.