Arimura had five birdies and a bogey and leads by one stroke over Choi Na-yeon. Choi had five birdies, including back-to-back at Nos. 16 and 17, and two bogeys in her 3-under 69.
World No. 1 Yani Tseng, who has four tournament wins already this year, is tied for third at 2-under. Karen Stupples, Karrie Webb and Yoo Sun-young are also at 2-under. Yoo had the only bogey-free round of that group. Tseng had three consecutive birdies from Nos. 7-9 among her six birdies on the day but also had four bogeys.
Arimura had a birdie at No. 2 and was still at 1-under after eight holes. But she posted birdies at the ninth and 10th holes and added two more at Nos. 12 and 14 before a bogey at 17 left her at 4-under.