Rosie Jones is two strokes off the pace at 10-under-par 134, while Michele Redman is three back at minus 9. Juli Inkster, Lorie Kane and Mi Hyun Kim are tied for fifth place at minus 7.
Kerr had an eventful day with three bogeys, two eagles and seven birdies. She started her round at Hiddenbrooke Golf Club by holing out from the fairway at the par-5 second for eagle.
After giving a shot back at the third, Kerr responded with a birdie at the fourth. She added back-to-back birdies from the seventh but stumbled again at the ninth with a bogey after she was unable to get up-and-down.
'I wasn't thinking very well out there,' said Kerr in reference to her bogey at the ninth. 'You can't miss short there. I talked my caddie into letting me take the club I thought I should take.'
Kerr continued her hot round with birdies on 10 and 12. She posted her final bogey on the par-3 13th as she three-putted the hole. Kerr later sank consecutive birdies beginning at the 16th. On the final hole, Kerr chipped in for eagle from the right rough giving her the course record.
'I had kind of a lull in the middle of the year. I think I got distracted from winning my first tournament,' said Kerr, who captured the Longs Drugs Challenge in April. 'So I got refocused on doing the small things well again. But now, I feel like I'm elevating my game to another level, doing the small things consistently well.'
Sorenstam started her day off on the wrong foot with a bogey at the first as she found a water hazard twice. She also bogeyed the ninth, but Sorenstam had carded three birdies between those bogeys to make the turn at seven-under.
The top-ranked player in the world continued her strong play with four birdies on the back nine, including Nos. 12 and 16, two of the three par-5s on the back side.
'Well, the way I'm hitting the driver, I'm playing the par-5s totally different than in previous years for me,' said Sorenstam, who was 4-under par on the par-5s on Friday. 'I'm going for most of them, and then I have a two-putt or a little chip. It really makes a difference.'
Sorenstam, who has eight wins so far this season, also said after the round that she is trying to chase some LPGA records.
'Mickey Wright has 13 wins, but Nancy (Lopez) had nine and then Kathy Whitworth has had 10, so those are numbers I have in my head,' said Sorenstam, who already owns the single-season earnings record. 'Well I was so-so about playing some events at the end of the year, but now I have a chance to break a record, I don't want to let it go.'
Se Ri Pak, a two-time winner of the LPGA Championship, is alone in eighth place at 6-under. Carin Koch, who went 5-0-1 in the Solheim Cup, rebounded with a second-round 67 to get to minus 4. Hee-Won Han was one shot further back at 3-under-par 141.
Paula Marti, Laura Diaz and Grace Park are tied for 11th at minus 2. Defending champion Dorothy Delasin shot her second straight even-par 72 and is alone in 14th.
Full-field scores from the Samsung World Championship