Munoz set the pace early -- she was in the first group off Thursday -- and was 7-under through 15 holes. She is two strokes ahead of Stacy Lewis, Phatlum Pornanong, Lizette Salas, Karin Sjodin and Yoo Sun-young, who are tied for second at 5-under 67.
Four more players, including world No. 1 Yani Tseng, are at 4-under and nine others finished at 3-under 69.
Munoz' first birdie came at the Par-3 second hole and she added two more at the fourth and seventh holes, which are both par 5s.
A birdie at No. 9 set off a string of birdies at the odd-numbered holes until she was 7-under through 15. Those last four birdies were all on par 4s.
None of the players tied for second managed to get around without a bogey. In fact, Sjodin had three bogeys against eight birdies. Twice she had three birdies in four-hole spans. She closed Thursday's round with her other two birdies.