Candie Kung posted a 66 of her own to finish two shots back at 4-under-par 136 alongside Catriona Matthew.
Sorenstam, who is making her first start on the LPGA Tour since missing the cut at the Women's British Open, has put herself in familiar territory. With one round to play, she will be gunning for her seventh victory of 2002.
'I've always said I want to be leading,' said Sorenstam. 'Tomorrow is a new day and anything can happen on this golf course. If I'm leading by one or tied with somebody, tomorrow is the day that counts.'
The 31-year-old was four shots off the pace through 18 holes at Tulsa Country Club and immediately began to make up ground with a chip-in birdie at the first.
Sorenstam ran into trouble with a bogey at the third after she failed to get up and down from off the green. She recovered at the par-4 seventh after she hit pitching wedge to nine feet for birdie.
At the par-3 ninth, Sorenstam knocked her tee shot to 10 feet for birdie to make the turn at minus-4. She added another birdie at the 11th to grab a share of the lead.
Sorenstam faltered with a two-putt bogey at the 14th, but the top player in the world responded with a birdie at the very next hole. She took the lead outright with a birdie at the par-5 16th, after she landed her third shot inside 12 feet.
Sorenstam, whose missed cut at the Women's British Open was her first since the 1999 U.S. Women's Open and just her fourth the last eight years, spent time in Europe after her disappointing outing at Turnberry. The Swede will look to make her first LPGA Tour appearance in four weeks a good one.
'I think I'm just going to go out tomorrow and keep playing aggressive,' said Sorenstam. 'I'm not going to worry too much about the other players. I just have to play my own game.'
Kerr used a key par save at the last to keep pace with Sorenstam. The 24-year-old pulled her drive and punched a 5-wood out of a bad lie. The ball landed just short of a bunker and she hit her third shot to eight feet where she made par.
'It was a very, very gutsy par,' said Kerr, who earned her first career win at the Longs Drugs Challenge in April. 'I've been in contention the last two weeks. I'll just go out tomorrow with the same game plan and see what happens.'
Kane had the low round of the day with a 64 on Saturday. The 37-year-old had seven birdies and one bogey to move into contention.
'I'm not surprised that a low round came out of me today, because I've been waiting for it for a while,' said Kane. 'Tomorrow I'm going to go out and do the same thing I did today.'
First-round leader Tracy Hanson struggled with a 3-over 73 to finish tied for sixth alongside Shani Waugh, Beth Bauer, Pamela Kerrigan, Joanne Mills and Kris Tschetter at 3-under-par 137.
Defending champion Gloria Park could not improve on her opening round. The Korean managed a 71 to finish nine shots off the pace at 3-over-par 143.
Full-field scores from the Williams Championship