Danielle Kang has played the brand of steady golf that wins on tough courses to secure the title by one stroke at the first LPGA Tour event in more than five months.
World No.4 Kang closed with a two-under 70 on Sunday to finish at seven-under 209.
She held off the challenge of France's Celine Boutier (71) while Australian Minjee Lee (70) was third at four-under for the week.
Lee reeled off three birdies in her final four holes, after dropping one shot on the front nine, to finish in style and leapfrog Yui Kawamoto (72) of Japan and Jodi Ewart Shadoff (75) of England.
The final round at drizzly Inverness Club in Toledo, Ohio, began with Kang, Boutier, and Britain's Ewart Shadoff all sharing the lead and ended in sunshine with the American on top.
"You have to respect the golf course and that's what I tried to do, even the little putts I didn't take for granted." – Danielle Kang
Kang and Boutier turned the final hour into a terrific duel with the Frenchwoman missing a short par putt on the 15th hole to fall one shot behind.
Boutier should have forced a playoff when she nailed her approach to four feet below the hole on the 18th but she made a tentative stroke on a tricky putt and the ball caught the left edge of the cup and spun away.
"I knew where I was standing with three holes left and I wanted to know where I was on the final hole stretch," Kang said.
"You have to respect the golf course and that's what I tried to do, even the little putts I didn't take for granted."
Kang won for the fourth time in her career. She has won in each of her last four seasons, starting with the Women's PGA Championship in 2017.
Nelly Korda, at No.2 the highest-ranked player in the field, tied for 40th.