Rachel Teske and Aree Song were three shots back at 6-under-par 66. Grace Park, who won the CJ Nine Bridges Classic last week, joined Karrie Webb, Lorena Ochoa, Laura Davies, Hee-Won Han and Akiko Fukushima in a tie for fifth place at 5-under-par 67.
Sorenstam, who opened with a 63 last year en route to her third consecutive victory at this event, began her run at a fourth straight title in identical fashion, although this time she had company after round one.
'I am very pleased, a little surprised but I will take it,' said Sorenstam. 'It seems like I like this golf course.'
She vaulted out of the gate with a chip-in eagle at the par-5 first at Seta Golf Club and drained a 12-foot putt for a birdie at the par-4 fourth to reach 3-under. Sorenstam then birdied two in a row starting at the par-5 sixth to go out in 31.
'I could not have asked for a better start,' said Sorenstam. 'I kept playing with a lot of confidence the rest of the way.'
Sorenstam tallied a birdie at the par-4 11th but cooled off soon after with four straight pars. The Swede caught fire down the stretch, however, with birdies on each of her last three holes to join Nakajima in the lead.
'I hit a lot of greens today and I remember doing that last year as well,' said Sorenstam. 'I just feel very comfortable on this course. I have been here so many times and have a good feel for it.'
Nakajima also had a quick start with a birdie at the first and back-to-back birdies from the fourth.
She made her move on the inward half starting with a birdie at the par-4 10th. Nakajima then birdied the par-3 12th and added a birdie at the par-4 14th to move to minus-six.
Like Sorenstam, Nakajima had a strong finish with three consecutive birdies to close out her round and match Sorenstam's course record from a year ago.
'I am excited to play with Annika,' said Nakajima. 'I am sure I will be very nervous when tomorrow comes.'
Becky Morgan, Lorie Kane, Young Kim, Heather Bowie, Yasuko Satoh, Michiko Hattori and Sakura Yokomine are knotted at 4-under-par 68.
Natalie Gulbis was one shot further back at 3-under-par 69 alongside Candie Kung, Catriona Matthew, Toshimi Kimura, Jamie Hullett, Noriko Aso, Midori Yoneyama, Chieko Amanuma and Junko Omote.