Sorenstam birdied the 18th to take her share of first while Kerr bogeyed the closing hole at Hiddenbrooke Golf Club. The duo stands three shots clear of Rosie Jones.
Se Ri Pak is tied with Michele Redman four strokes back at 11-under-par 205. Juli Inkster and Lorie Kane are tied for sixth place at 9-under-par 207. Mi Hyun Kim is one shot behind that pair at minus-8.
Kerr, who had been in control of the tournament most of the day, lost the outright lead with a bogey on the final hole. That bogey was her third on the back nine to go along with four birdies.
'That's not a good way to end a round,' said Kerr, who posted a 3-under 69 on Saturday. 'But when you bogey the last hole, you don't think about it. So I'm just not going to worry about it.'
Kerr had a much steadier front nine with two birdies and seven pars. The birdies came at the par-5 second and the par-4 seventh.
Sorenstam started her round with a birdie at the fifth and added another at the eighth. She ran into trouble with a bogey at the ninth to make the turn at 12-under.
The Swede began her run to the top of the leaderboard early on the inward half with back-to-back birdies from the 10th. She bogeyed the 12th but responded with a birdie at the 16th. Sorenstam, who is looking for her ninth victory of 2002, then birdied the 18th to tie Kerr for the lead.
'I'm just going to continue what I have done in the past,' said Sorenstam. 'Hopefully things will come up the way it has most times for me.'
Carin Koch sits alone in ninth place at 7-under-par 209. Paula Marti is one stroke behind Koch in 10th place.
Defending champion Dorothy Delasin, Rachel Teske, Grace Park and Laura Diaz are tied for 11th place at 4-under-par 212. Teske's 5-under 67 tied Pak for the low round of the day. Hee-Won Han is one shot further back at 3-under-par 213.
Karrie Webb, the 2002 Women's British Open champion, collected five birdies and one bogey for a round of 68. The Australian finished alone in 16th at 2-under-par 214. She was followed by Kelly Robbins at 3-over-par 219.
Beth Daniel, who captured the inaugural event in 1980 and successfully defended her title the following year, carded an even-par 72 to finish alongside Mikino Kubo and Mi Na Lee at 4-over-par 220.
Full-field scores from Samsung World Championship