Inbee Park, seeking a third victory of the year and trying to catch Stacy Lewis in the LPGA Player of the Year race, seized a two-shot lead at the Lorena Ochoa Invitational.
South Korea's Park had six birdies -- three on the front nine and three on the back -- in her six-under 66 for a 54-hole total of 15-under par 201 at the Guadalajara Country Club.
"I had a really solid day today," Park said, adding that back-to-back birdies to open the round "makes the day really easy".
She was two shots in front of American Cristie Kerr, who carded a 67 for 203. South Korea's So Yeon Ryu also posted a 67 for 204 and American Angela Stanford, who held a one-shot lead over Park going into the third round, posted a 72 for 205. Next came France's Karine Icher after a 69 for 207.
Lewis, ranked second in the world and coming off an LPGA-leading fourth title of the year in Japan last week, was tied for sixth on eight-under 208, alongside American Michelle Wie, Taiwan's Candie Kung and South Korean Hee Kyung Seo.
Lewis, who is trying to become the first US golfer to win the points-based Player of the Year award since Beth Daniel in 1994, carded a 71.
Park, who won the Evian Masters in France in July and the LPGA Malaysia last month would have to win this week and at next week's season finale even to have a chance to pass Lewis for Player of the Year honors.
Park said she was trying to focus only on her game, and not on her chances of overtaking Lewis in the race for Player of the Year, which remain slim even if she wins.
"I mean, I can't expect Stacy to play bad two events in a row," she said. "So I mean, even if I don't win Player of the Year, I've had a really great season and I'm really satisfied with myself."
Park currently leads the money list, as well as the race for the Vare Trophy for the player with the lowest scoring average.
"That would be two big achievements this season," she said. "If I win three (awards), I don't have anything else to do next season so it's kind of good to have one, maybe, or two and take it one step at a time.
"I'm not going to play golf this year, then quit," she added. "I have a lot of years in front of me."