The 31-year-old, U.S.-based Sergas led by three shots after a first-round 64 and had a two-round total of 11-under 133.
Kristie Smith of Australia was in second after a 64, posting nine birdies and a bogey in a round which lifted her nine places up the leaderboard.
Linda Wessberg of Sweden shot the day’s best round of 63 to sit in third place on 9-under 137, four shots behind Sergas.
Smith was a late starter on the tournament’s first day and struggled to a 1-under 71 in strong winds. She made the best of an early tee time Friday, with her only mistake a three-putt at the par-3 15th.
“That came out of the blue because I was playing well and had holed some great putts,” Smith said. “I didn’t really hit it close, but put it close with my wedges when I needed to and made the putts when I needed to.”
Thirteen-year-old New Zealand amateur Lydia Ko was among a group of four players in fourth place at 6 under, along with British veteran and defending champion Laura Davies. Ko had a 68 Friday and Davies shot a 66.