On a historic day when women's professional golf made its debut at St. Andrews, the 25-year-old Mexican star set out to make history for herself. The No. 1 player in the world made three straight birdies around the loop starting at No. 8 and kept bogeys off her card to keep her name atop the leaderboard among early finishers.

"It was just a really good day, one of those days when things are easy and really good," Ochoa said. "There was only a little bit of a breeze, and I took advantage of that and made some birdies.

"I had in my head 2 or 3 under, so it's even better than I thought.

A Swede was two shots back and it wasn't Annika Sorenstam.

Louise Friberg, who is yet to win a tournament, made six birdies in her 69, which was spoiled by two bogeys on the back nine. Sorenstam, the 10-time major winner, birdied the last two holes for a 1-under 72.

Ai Miyazato of Japan shot 70.

In perfect weather at the home of golf, Ochoa birdied three straight holes and stretched her lead to three shots when her long approach to the 15th settled 2 feet from the pin.

That was her fifth birdie, and another followed at the 17th, the tough Road Hole which has been made a par 5 for the Women's Open.

Ochoa's second finished at the back of the green and her first putt left her with a 5-footer for birdie. After Miyazato bogeyed the 16th, Ochoa walked onto the 18th green four ahead of the field, then narrowly missed a 15-foot birdie on the final hole.

Miyazato recovered from a double bogey seven at the fifth to make four birdies on the back nine. The Japanese star drove into rough at the fifth, failed to clear a pot bunker with her second and had to play her third shot sideways out of the sand.

After winning her first title at the Evian Masters on Sunday, Natalie Gulbis didn't expect to be 5 behind at the turn. Without a birdie on the front nine, the American was 1 over after her bogey 5 at the second and went on to make an even par 73, along with Paula Creamer.

U.S. Women's Open champion Cristie Kerr struggled to a 77, beginning her round with two bogeys.

"I've been putting way too much pressure on myself since the Open and it has backfired on me," she said. "I'm pushing it way too hard."