Miyazato made light work of the strong winds as she shot a two-under-par round of 70 to overhaul Meena Lee, who lead early on the back nine.
Lee, who also briefly tied for the lead after a birdie on the 15th hole, also finished with a final round of 70 to tie for second with Azahara Munoz.
“I don’t know what happened,” Miyazato said.
“I just focused on my game. I was pretty nervous toward the end because I know everyone is playing so well. I had to finish really strong.”
Miyazato lead by three shots heading into the final round but lost her lead after a bogey at the par-three 12th.
Lee three-putted at the 14th for a bogey to lose her advantage before briefly drawing level again one hole later.
But a wayward approach shot on the 18th from Lee saw her three-putt for a double bogey, ending her chances of victory.
“But I was a little bit downwind,” Lee said. “I tried to go for the pin and I end up three-putting. I tried.”
World number one Yani Tseng overcame an ankle injury to shoot a final round 74 and tie for 10th, to continue her run of finishing inside the top 10 in all seven of her LPGA starts this season.
“I didn’t play well today,” Tseng said. “I didn’t give myself lots of chances to make birdie. I don’t know what happened. My distance was way off. Just not my day out there.”