Although the 25-year-old ace Filipina shotmaker jumped from her previous ranking of No. 15, Rosales stood seven shots adrift of joint pacesetters Han Hee-won and Meg Mallon as the two leaders shot 68 and 65, respectively, to pull away by five strokes from third-running Cindy Figg-Currier, who struggled with a 73.
Rosales, chasing a fifth top 10 finish in 15 tournaments in the lucrative circuit, holed out with a birdie on the 18th of the par-71 Wykagyl Country Club course to save a round of 33-36 for a 54-hole aggregate of 209.
That was seven strokes off Han and Mallon who set up a virtual one-on-one duel for the crown by posting identical 202s. Figg-Currier was far behind by five at 207 while Korean Kim Mi-hyun stood a shot farther back at 208 after a 71.
Just two strokes behind Figg-Currier, Rosales is expected to go flat out to at least snatch the third place honors and hopefully, the title with a solid finish coupled with a floundering windup by the joint leaders.