Creamer was joined at 6-under-par 138 by Sophie Gustafson (70) and first-round co-leader Annika Sorenstam (71).
Women's British Open winner Sherri Steinhauer fired the low round of the day to move into fourth place. She posted a 5-under 67 to end at minus-5.
Lorena Ochoa, who shared the lead with Sorenstam after the first round, struggled to a 1-over 73. She shares fifth with Kraft Nabisco champion Karrie Webb (69).
Michelle Wie had another adventurous day en route to an even-par 72. She double-bogeyed the third, but got those strokes back with birdies on five and eight.
The 17-year-old birdied 12 and 14, but bogeys on 13 and 15 left her at plus-2. She finished there as she parred the final three holes. Wie is tied for 15th with Natalie Gulbis.
Early on during round two, it looked like the Swedes -- Sorenstam and Gustafson -- were going to run away from the field at Bighorn.
Sorenstam, the defending champion and five-time winner here, birdied the second, then got up and down for birdie from a bunker on the third to move to 7 under. She nearly holed her second shot at the par-4 fifth, but settled for a kick-in birdie that got her to minus-8.
Gustafson opened with a birdie on the third. She birdied the fifth and sixth, then made a 3-footer for birdie on seven to join Sorenstam at minus-8.
The 32-year-old Gustafson stumbled to a bogey at the par-3 eighth to fall out of the lead. Sorenstam also bogeyed the eighth, then faltered to a double-bogey on nine to slide to minus-5, two behind Gustafson.
Sorenstam inched back within a stroke when she sank a 6-footer for birdie on 12. Gustafson came up short of the 13th and was unable to get up and down for par. Sorenstam pitched to 12 feet on 13, but missed the par-saving putt to again fall one back.
Gustafson could not get up and down from a bunker on 14 and that bogey dropped her to minus-5. She shared the lead with Steinhauer and Sorenstam at that point.
Steinhauer birdied the third and fifth and sank a birdie effort on the par-3 eighth. Around the turn, Steinhauer birdied 12 and 15 to move to minus-5. She parred the final three holes to finish there and close a bogey-free round.
Creamer, meanwhile, carded three birdies on the front nine to climb to minus-5. She parred six in a row from the eighth, before struggling to a bogey at 14.
The reigning LPGA Tour Rookie of the Year birdied the 15th to get to 5 under and into a share of the lead with Gustafson, Steinhauer and Sorenstam.
Both Gustafson and Sorenstam birdied the par-5 15th to move to minus-6. Gustafson stumbled to a bogey on 16 as her 14-foot par putt lipped out.
Creamer, playing one group ahead of Gustafson, closed with a 12-foot birdie putt to get into the clubhouse at minus-6.
Gustafson rebounded from her bogey on 16 by making a 4-foot birdie putt on 17 to join Sorenstam and Creamer at minus-6.
Sorenstam missed a short par putt on 17 to slip one back. She atoned for that mistake by knocking her approach within inches of the hole at the last. Sorenstam tapped in the birdie putt for her share of the lead.