Higa and Ichinose each had 6-under-par 66s while Oyama, the first-round leader, shot a 68 Saturday for a 36-hole total of 8-under 136 with one round to play.
They are one stroke up on Asako Fujimoto (67 Saturday) and Brittany Lincicome (68) with four more players tied for sixth at 6-under. Defending champion and world No. 3 Stacy Lewis is in a group of five tied at 5-under. Lewis overcame a seven-shot deficit in winning the tournament in 2012.
Higa's 66 was bogey-free. She scattered three birdies over the first 13 holes but then ran off three consecutive birdies for her share of first.
Ichinose posted back-to-back birdies at Nos. 3 and 4 and then had four straight on 7-10. She got to 7-under on the day with a 14th-hole birdie but slipped back with a bogey at 17. It was her first bogey of the tournament.
Oyama also had one bogey Saturday, that coming at the 15th hole. She was 5-under prior to that.