Creamer and Park both fired a 5-under 67 at the Bighorn Golf Club's Canyons Course.
World No. 1 Lorena Ochoa appeared headed for the first-round lead before she double-bogeyed the closing hole to shoot a 68. That left her tied for third with Mi Hyun Kim and Kraft Nabisco winner Morgan Pressel.
Michelle Wie, who has struggled with injuries and high scores as she tries to live up to her early superstar billing, was unable to properly celebrate her 18th birthday. She shot a 79 and was in last place by three shots.
Wie accepted a special invitation to be a part of the 20-player field. The decision was not a popular one among her fellow players since Wie has made only two cuts this year and won less than $10,000 in seven LPGA Tour events.