England’s Charley Hull finished alone in fifth after a round of 73, but Australia’s Gabriela Ruffels carded a fine 68 to tie for sixth with South Korean Jin Young Ko, eight shot backs at seven under.
Australia’s two-time major winner Minjee Lee, who had a share of the lead heading into Saturday’s play, fell back with a final-round 78 to finish joint-12th on two under.
Germany’s Esther Henseleit, the silver medallist at the Paris Olympics, was a runner-up again. After playing at par on the front nine, Henseleit (70) had three birdies and a bogey on the back nine to narrow the gap with Coughlin, but she couldn’t catch her.
After her slow start to her round, Coughlin added five birdies - including at the 14th, 15th and 18th - to cruise to the win. She single-putted the final seven holes, effectively ending the dreams of her competitors.
Coughlin admitted her recent success on the LPGA Tour is “incredible.”
“I think if you would have told me (of her future wins) - I mean let alone at the beginning of this year but probably the beginning of last year - I probably wouldn’t believe you at all that this is what I’ve just done,” she said.
“I played super solid all four days and just kind of tried to let the wind do what it did and not try to fight it too much.
“I was able to kind of just hit the ball where I was trying to most of the time and good distance and then make some putts.”