'You can't really examine it too much, because there is a mystical element to it that you can't put your finger on,' Kerr said after shooting a career-best 10-under 61 in the second round.
After rolling in a 35-footer at the 13th, she showed off a lasso move for the gallery.
'[W]hen you're shooting a low round you just know everything's going to go in. I don't know how to explain it,' said Kerr, whose previous low round was a 62 at the 2005 Longs Drugs Challenge.
'I wanted to give the crowd a little acknowledgment that I knew they were there. It's business out there, definitely, but that was a lot of fun to make that putt the way I did. And I just wanted to let them know that I knew they were there.'
Kerr stole the show from Sorenstam, the two-time defending champion who has won this event three of the last five times it has been held. Sorenstam had a 3-under 68 on Saturday after opening with a 64 on Friday.
Playing one group ahead, Sorenstam began following Kerr's progress.
'[At] the seventh or eighth hole I started to see Cristie's name up there and then I saw she was 8-under when I was nine...and then all of a sudden she's at 11,' recalled Sorenstam, who is at 10-under 132.
'I think Cristie obviously had a fantastic round and made my round not look so great. But I'm happy with 68.'
Tied for 13th place overnight, Kerr had to make a 10-foot putt to save par at the first hole. Then, she turned it on.
Kerr began climbing the leaderboard with three consecutive birdies from the second hole -- all on putts within 7 feet. She added a 10-foot birdie putt at the sixth, a 30-footer at the seventh and a 25-footer at the ninth to make the turn at 7 under.
'[I]t was kind of a shaky start on the first hole,' Kerr said. 'Then I got in a groove with my swing and hit it close a bunch of times and made a bunch of close putts, made some really good putts.'
Kerr birdied the 10th from 7 feet, then made putts of 30 and 35 feet at the 12th and 13th. She found her final birdie at the par-5 14th after she knocked a wedge within 9 feet.
'I knew I had to shoot 4- or 5-under to move up, to have a chance for tomorrow,' said Kerr, a two-time winner this season. 'So to shoot 10-under is absolutely an added bonus, gravy. I love the position I'm in.'
Sunday, it'll be Kerr and Sorenstam in the final pairing.
'I expect a lot of birdies,' Sorenstam said. 'It'll be fun.'
Allison Hanna is alone in third place at 5-under 137 following a 69.
Tour money leader Lorena Ochoa had a second consecutive 69 and shares fourth place with Diana D'Alessio (72) and Jill McGill (71).
The cut fell at plus-4 with 73 players moving on to Sunday.