Grace Park was one shot back at 10-under-par 134 while Laura Davies followed at 9-under-par 135.
Sorenstam was two shots off the lead to start the second round on the Championship Course at Moon Valley Country Club. The Swede knocked a sand- wedge to five feet for a birdie at the first and added a birdie at the sixth to move to 7-under.
She dropped a shot with a bogey at the seventh but recovered on the back half. Sorenstam birdied the 10th and the 13th before a remarkable stretch to close her round.
Sorenstam hit a pitching-wedge to two feet at the 16th and drained a three-footer for a birdie at the very next hole. At the par-4 18th, the top player in the world drained a 10-foot putt for her third birdie in a row.
'I'm very pleased where I'm at,' said Sorenstam. 'I'm happy to be back and happy that my game is here as well.'
Sherri Turner, Angela Stanford and Dorothy Delasin finished three shots off the lead at 8-under-par 136.