The American had started the day just off the pace set by overnight leader Chella Choi, but soon worked her way up the standings, with four birdies and two bogeys in a score of two-under 70.
That left Pressel on six under for the tournament at Locust Hill Country Club and with a narrow advantage over South Korean pair Inbee Park and Choi.
Park enjoyed her day on the course with a four-under 68, while Choi was one over for the round after mixing two birdies with three bogeys.
Scotland's Catriona Matthews was the leading European, four shots off the lead, after shooting a second consecutive one-under 71.
Wet weather on Thursday and Friday meant the second round could only be completed today, with organisers aiming to squeeze 36 holes into the final day's play.