Laura Diaz posted a 6-under-par 65 in round one and stands alongside Amy Hung and Seon-Hwa Lee in a tie for third place on the Bay Course at the Seaview Marriott Resort & Spa.
Sorenstam, who has won this crown three times including last year, was steady to start her round. She was 1 under through eight holes with her lone birdie coming at the par-5 third.
The Swede then drained a 7-foot eagle putt on the par-five ninth to make the turn at minus-3.
'I hit a 5-iron to 7 feet and rolled that putt in for eagle,' said Sorenstam, whose lone win this season came at the MasterCard Classic, her first event of the year. 'I just hit a lot of good shots to the center of the greens. I played smart today.'
Sorenstam came right back with a birdie on No. 10 as her approach stopped 7 feet from the hole. She moved to 5 under as her 8-foot birdie effort on the 13th found the bottom of the cup.
The women's world No. 1 rolled in a 30-foot birdie at the par-3 15th to get within one of Redman's lead. Sorenstam grabbed a share of the lead with a tap-in birdie on the par-5 closing hole.
'I'm very happy with the round. I thought I played some good golf today,' Sorenstam said. 'The mixture of good drives and good shots and I rolled in a few putts, so I'm very pleased.'
Redman, played the back nine first on Friday, and collected her first birdie on the 12th after hitting a wedge to 20 feet. She parred the next five holes before an up-and-down birdie on 18 put her at minus-2.
The 41-year-old started a run of birdies at the second when her 12-foot try fell into the cup. Redman two-putted for birdie on the third to get to 4 under. She made it three straight with a birdie on the fourth.
Redman, who claimed the last of her two tour wins at the 2000 Betsy King Classic, birdied No. 5 from 3 feet out. She ended a run of five straight birdies as her 12-foot putt at the sixth fell into the cup.
'I did really good. I finally starting making some putts,' admitted Redman. 'The last two months my putting has just really hurt me. I'm trying to be more relaxed with the putter.'
Defending Women's British Open champion Jeong Jang carded a 4-under-par 67 on Friday. She shares 13th place with Minea Blomqvist, Diana D'Alessio, Sung Ah Yim, Aram Cho, Mi Hyun Kim, Stephanie Louden, Patricia Meunier-Lebouc and Becky Morgan.