Ammaccapane's overall total is 6-under 138. She has never won a tournament on the LPGA Tour and this is her first 36-hole lead.
Her best career finish this season was a tie for 10th place at the Fields Open in Kapolei, Hawaii, in February.
"I feel like I'm hitting it well enough to score," she said after a round that started with a par at the first hole and a three-putt bogey at No. 2. "The driver's been really well, so let's see if I can keep (the ball) in the fairway. The last two days were a test."
2007 winner Young Kim (74) missed the 2-over 146 cut.