Shi Hyun Ahn, an LPGA Tour rookie, carded a 6-under 66 to climb into second place at 14-under-par 202. Cristie Kerr is one stroke further back at minus-13.
Laura Davies and Grace Park posted rounds of 68 to move into a share of fourth place at 11-under-par 205. They were joined there by defending champion Se Ri (70) and Lorena Ochoa (69).
Sorenstam opened with a one-stroke lead and quickly extended that as she chipped in for eagle at the second. She cruised around the turn with nine straight pars.
'I was happy with the start,' Sorenstam said. 'I made eagle on the second hole to kind of get me going a little bit. Then in the middle of the round I was struggling a little bit with my shots, but I hung in there.'
The Swede faltered to a bogey at the 12th after missing the green at the par-3. It was then that she was briefly tied atop the leaderboard by Kerr at 13 under.
However, Sorenstam, who won this event in 2001, reclaimed the lead with an up- and-down birdie at the 14th. At No. 17, she drained a 13-foot birdie try and closed her round in style as she rolled in a five-footer for birdie at the last.
'I thought I made good par putts when I needed to and obviously to finish birdie-birdie helps,' said Sorenstam, who tied for third here last year. 'I feel better about my game now.'
Ahn, who won the CJ Nine Bridges Classic last year to gain status on the tour, was four shots back to start her round. She fell further back when she bogeyed the first but came right back with a birdie at the next.
The Korean birdied the sixth, then converted back-to-back birdies from the ninth to get to 11 under. Ahn birdied Nos. 14, 16 and 18 down the stretch to claim second place.
'I want to take it step-by-step,' said Ahn through a translator. 'I'm looking for a lucky first year.'
Kerr opened one shot behind Sorenstam and picked up a birdie at the third. She dropped a shot at the ninth, but fought back to grab a share of the lead with back-to-back birdies from the 10th.
Kerr kept pace with Sorenstam, who had moved ahead of her, with a birdie at the 16th. However, Kerr dropped a shot at the last to finish three back heading to the final round.
'I didn't play as well as I would have wanted today, but I made some birdies,' Kerr said. 'I made some putts, and really the only bad thing about my round was my drive on 18.'
Heather Bowie posted a 3-under 69 to move to 10-under-par 206.
Teenage amateur sensation Michelle Wie continued her solid play as she shot a 2-under 70. She stands alone in ninth place at 7-under-par 209.
'I think today was the hardest of the three rounds I've played,' Wie said. 'I went into the rough a lot. I didn't really hit my driver as good today and got some bad lies in the rough.'
Wendy Ward posted a 4-under 68 to climb to 6-under-par 210. She is joined there by Rosie Jones, Lorie Kane, Michele Redman and Donna Andrews.