Defending Women's British Open champion Jeong Jang posted a 6-under-par 66. She is tied for third with Virada Nirapathpongporn, Kristin Tamulis, Brandie Burton and Hee-Won Han.
She then birdied the par-5 fifth to move to minus-2. Scranton made the turn at 3 under thanks to a birdie on the ninth. Around the turn, she dropped in a 20-foot birdie putt on the par-3 11th.
Scranton birdied the 13th, then carded back-to-back birdies from the 15th to reach minus-7. The 45-year-old dropped a shot on 17 when her approach came up short of the green, but atoned for that mistake with an 8-foot birdie putt at the last.
'I hit it quite well today. It's funny how sometimes you have a really good day that seems so easy,' Scranton stated. 'I drove it quite well. I missed just two fairways and both of those led to bogeys. Other than that, I had a lot of birdie opportunities. It was just pretty easy.'
Lee, whose other tour win came last year at the Canadian Women's Open, parred her first six holes as she started on the back nine.
The Korean faltered to a bogey on the par-4 16th after missing the green to the right. Lee birdied the next two holes, both from 18 feet out, to make the turn at 1 under. She started a great run at the second.
Lee two-putted for birdie on the par-5, then made it two straight with a 15-foot birdie putt on the par-3 third. She birdied the fourth, then converted her fourth straight birdie effort on the fifth.
The 24-year-old made it five in a row as she birdied the par-4 sixth. Lee made pars on seven and eight before a birdie on the par-4 ninth got her to minus-7.
'I had a great day,' Lee said. 'I played very good on the first nine, but I played better on the back nine. Everything worked out.'
Sophie Gustafson posted a 5-under-par 67 to share eighth place with Mikaela Parmlid, Marcy Hart, Liselotte Neumann and Vicki Goetze-Ackerman. Natalie Gulbis leads a group of seven players one stroke further back at minus-4.
Defending champion Jimin Kang opened with a round of even-par 72 and stands in a tie for 63rd place.