Myerscough shot an even-par 72 to grab a one stroke advantage over Naree and two stroke advantage over Aree as they head into Saturday's final round.
Naree, the defending champion, leapfrogged over her sister and into second by firing a even-par 72. Naree has improved her scores each day, going 77, 74, and 72.
Aree, who had a two stroke lead after the second round, followed up her 72 on Thursday with a 4-over 76. Aree, who like her twin sister Naree, both hail from Bradentin, Fla.
Robin Burke(74) and Corey Weworski(75) are in a tie for fourth at 10-over-par 226.