After Thursday's play was scrubbed following lightning and torrential rain, Pressel led the morning wave with a four-under-par 68, taking advantage of soft greens for a one-shot lead over fellow American Brittany Lincicome.
Another stroke back were South Korean Hall of Famer Pak Se Ri and American Jessica Korda, who shot rounds of two-under 70.
Among the afternoon starters were defending champion Shanshan Feng of China and seven-times major winner Karrie Webb of Australia. The 38-year-old Webb is coming off a victory in last week's ShopRite Classic.
Despite 2.5 inches of rain dumped on the layout of the year's second major championship, groundskeepers were able to prepare the course for play after getting to work at 4 a.m. (0800 GMT)
Pressel said she was surprised to tee off as scheduled.
"I thought that we would probably tee off at about noon, having seen photos of what the golf course looked like," said Pressel. "And it didn't stop raining just about all night.
"But the ground staff here did an incredible job getting the course ready. I don't think the greens could be any more perfect. There's some casual out there but that's to be expected. We're just happy to get out on the golf course.
Three tees were moved forward in consideration of the conditions and hitting fairways became a key with the water-logged rough even more penal than usual.
"The rough is nasty," said Korda, who had five birdies and three bogeys.
The leaderboard demonstrated that short hitters like Pressel and bombers such as Korda and Lincicome all had a chance to score at Locust Hill.
"If you don't hit the fairway you can be as long or as short as you want, but it's still going to play at a disadvantage," Korda said about settling into the rough. "That ball sits down, you can't even get it out."
Organizers planned to stage the second round on Saturday and squeeze in 36 holes to finish up on Sunday.
Three shots off the pace at 71 were 2009 champion Anna Nordqvist of Sweden, 1994 and 1996 winner Laura Davies, Catriona Matthew of Briton, South Korean Amy Yang and 18-year-old American Lexi Thompson.
(Reporting by Larry Fine in New York; Editing by Frank Pingue)