Hjorth, Choi Na-yeon, Brittany Lang and Dewi Claire Schreefel each had six birdies and a bogey Thursday in shooting 5-under-par 66. They are tied for the lead, one stroke ahead of Paige Mackenzie and Azahara Munoz.
Five more players are tied for seventh at 3-under 68.
Hjorth had three consecutive birdies over Nos. 3-6 and added three more over a four-hole span to get to 6-under for the round after 12 holes. However, she finished with five pars and an 18th-hole bogey to slip into the tie for first.
Choi, the world No. 4-ranked player, went the other way. She opened with four pars and had a bogey at No. 5. But she then had three straight birdies and grabbed a share of the lead with three birdies over Nos. 14-17.
Lang's lone bogey came at the 11th hole and it was birdies at 16 and 17 that moved her into first. Schreefel, who had a bogey at 14, finished with a birdie at 18 for her share of first.