Overnight leader Song Bo-Bae of South Korea hit a four-under-par 68 to stretch her lead and win the US LPGA Tour Mizuno Classic golf tournament on Sunday.

Starting the day with a one-stroke lead, the 23-year-old Korean sank five birdies against one bogey for a three-round total of 15-under-par 201, three strokes clear of the field.

"I couldn't sleep last night, because I was so nervous. (But) I started hitting balls well since last week, and that led to this victory," said Song.

She said she became sure of victory only at the 17th hole, "when my tee-shot went towards the bunker, but the ball luckily bounced back and stopped 15 feet short of the cup.

"A lot of the other players were chasing up, and I felt nervous. Mistakes are inevitable in golf, so I tried to play (with) as few mistakes as possible," she added.

The win was Song's second of the season, following her victory at the Japan Women's Open last month and her third overall on the Japan tour, earning herself the winner's cheque of $US210,000 ($A230,000) dollars.

With the win, Song has won exemption from the US LPGA Tour but she did not say whether she would now move to the US from Japan.

"I've played in several big tournaments when I lived in Korea, but I felt that Japan suits me more. So I still don't know yet," said Song.

World No.1 Lorena Ochoa of Mexico fired a bogey-free eight birdies for a 64 to share second place on 204 with Park Hee-Young of South Korea and American Brittany Lang.

"I scored 64, which was very good, and now, I can go home happily. I just thought about doing my best today. I played aggressively and that led to the runner-up finish," said Ochoa.

Defending champion Shin Ji-Yay of South Korea tied for fifth place on 205 with Tseng Yani of Taiwan and compatriots Jeon Mi-Jeong and Park Inbee.

Japan's Momoko Ueda, the 2007 champion, and Rui Kitada, along with Kim In-Kyung of South Korea, were one stroke further back.