Women's world No. 1 and defending champion Annika Sorenstam is one stroke back at minus-6. She was joined there by Patricia Meunier-Lebouc and Candy Hannemann.
Sorenstam, who has struggled since her win at the MasterCard Classic in March, three-putted for bogey on the first. She came right back with a 4-foot birdie putt on two to erase that early mistake.
The Swede knocked her second shot to the par-5 sixth within tap-in range. The eagle got Sorenstam to minus-2, but she fell back to even-par with bogeys on eight and 11.
Sorenstam, however, turned it on after her third bogey. She sank 5-foot birdie putts on 12 and 13, then chipped to a foot at the 14th to get to minus-3.
A 10-foot birdie try on 16 and a 12-footer on 17 moved Sorenstam to 5 under. She made it three straight to close her round with a two-putt birdie at the last to end one back.
'I'm happy with my day. I made a lot of birdies and an eagle, but I did make a few mistakes,' Sorenstam commented. 'Three bogeys out there, but overall to comeback after weeks off, I played solid.'
Kerr got her round going with an up-and-down birdie on the par-5 second. She took advantage of the next par-5, No. 6, with a two-putt birdie.
The 28-year-old ran home a 20-footer for birdie on the eighth to move to minus-3. Around the turn, Kerr sank a 7-foot birdie putt on the 10th. She two-putted the 13th, also a par-5, to get to 5 under.
Kerr, a six-time winner on tour, came right back with a birdie on the 14th. She dropped her approach within 6 feet at the 17th, setting up her final birdie. Kerr had birdied the first three par-5s, but could only par the par-5 closing hole.
'I switched putters this week to get a better alignment,' Kerr said. 'The new putter gave me a completely different feel. I hit it fairly decent today. I gave myself a lot of opportunities, which I was able to capitalize on.'
Hjorth started her round the same way as Kerr with an up-and-down birdie on the second. She collected her second birdie on No. 4 when she ran home an 18-foot putt.
The 32-year-old birdied six and seven to get to 4 under. Hjorth parred her next five holes around the turn. She ran in an 8-footer for birdie on 13 and came right back with a 10-foot birdie putt on 14. Hjorth closed with a 15-foot birdie putt at the last to share the overnight lead.
'Shooting 7 under is always fun,' said Hjorth, whose two tour wins came in 1999. 'I have had a few tournaments where I have done well in the first round, and I haven't been able to keep it up. So hopefully this week I can keep it up.'
Paula Creamer, the 2005 LPGA Tour Rookie of the Year, is one of 11 players tied for 13th place at 4-under-par 68.