Buhai stumbled with three bogeys in five holes. The 30-year-old South African, who has never won on the LPGA Tour, had a 72 to drop to second at 12 under.
“I played my first nine holes probably the best ball-striking I could have had. Hit really good shots,” Buhai said. “Turned 2 under, birdied my 10th to go to 3- nder and hit two poor wedge shots on 11 and 12, normally my strong point. Let the three-putt rattle me on No. 12.
“I’m still here, two shots behind going into the final round playing in the final group. If you told me at the beginning of the week, I would have taken it.”
Second-ranked Sung Hyun Park was another shot back after a bogey-free 68.
Top-ranked Jin Young Ko and Americans Morgan Pressel and Lizette Salas were tied for fourth on 10 under. Ko (68) is seeking her third major title of the year after winning the Evian Championship last week in France. Pressel had a 66, and Salas shot 70.
Defending champion Georgia Hall was 10 shots back after a 74.