"Everything fell together -- ball striking, putting," she told reporters after posting a 10-under 134 total, one stroke ahead of South Korean Kim Hyo-joo (67) and Thai Patcharajutar Kongkraphan (66).
Another Thai, Ariya Jutanugarn, has dominated the LPGA recently, with five victories since May, including the Canadian Women's Open on Sunday, and she remained in contention for another win, four strokes behind after a 68.
Alex, 78th on the LPGA money list, heads into the final two rounds in search of her maiden LPGA victory.
"This I think is the lowest I've shot out on the LPGA ... definitely the best round I've played in a long time," she said after finishing with a flourish, sinking a long birdie putt at her penultimate hole, before striking a nice five-wood into the par-five ninth.
"It is a pretty wide-open course, which is sometimes for me a little challenging because it's hard to pick out targets.
"But I'm trying really hard to focus, be as narrow as possible off the tee and into the green and just be very specific with what I'm trying to do."
Patcharajutar is also in pursuit of a first LPGA win, and she is feeling better about her game with a new set of clubs.
"From last week, I have so much more confidence," she said, disclosing she also had a local police officer working as her caddie this week.
Alena Sharp (70) was the best-placed Canadian, five shots behind, while world number one Lydia Ko (72) ended the round eight strokes off the pace.
(Reporting by Andrew Both in Cary, North Carolina; Editing by Mark Lamport-Stokes)
