Hjorth was 6 under after shooting her second consecutive 68. Lee, the co-leader after the first round, shot 70 with two birdies and a bogey.
Song-Hee Kim of South Korea had a 68 and was one shot behind heading into Sunday’s final round.
Natalie Gulbis (68) and 50-year-old Juli Inkster (67) were tied for fourth, two shots behind the leaders. Inkster had five birdies and a bogey the second hole.
Hjorth, looking for her first LPGA win since 2007, said she made a putter change this week following some recent missed cuts. She eagled the par-5 sixth hole and had five birdies.
Play was suspended for nearly 2 1/2 hours because of an afternoon lightning storm.
First-round co-leader Mika Miyazato had a 72. Michelle Wie shot 74 to trail the leaders by six strokes. She had a bogey on No. 1 and added three more before a birdie on 16.