Kerr set a course record and an 18-hole tournament scoring record, and set a 36-hole scoring record by finishing the second round at 11-under 131. Among her 10 birdies, four came on putts of 25 feet or more.
"When 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.
Sorenstam, the two-time defending champion who has won this event three of the last five times, had a 3-under 68 on Saturday after opening with a 64 Friday.
Allison Hanna (69) is alone in third place at 5-under 137. Tour money leader Lorena Ochoa had a second consecutive 69 and shares fourth place with Diana D'Alessio (72) and Jill McGill (71) at 4-under 138.