Regularly sinking putts of 15 feet or more, Sorenstam had eight birdies and tied the course record for the 6,602-yard Cedar Ridge Country Club, set in the tournament's opening round last year by Maria Hjorth.
Dina Ammaccapane and Jill McGill are tied for third at 4 under. Two others, Michele Redman and Allison Hanna, are at 3 under and the LPGA's leading money-winner this year, Lorena Ochoa, and Paula Creamer are among a group of six golfers at 2-under 69.
Sorenstam won the tournament the last two years at Cedar Ridge, in suburban Tulsa, and also in 2002, when it was played at Tulsa Country Club. She's also won the last two tournaments in which she's played, the State Farm Classic last week in Springfield, Ill., and the TPC of Scandinavia in her native Sweden.
All that while trying to fix what she says is a flaw in her swing.
There weren't many flaws apparent in her game Friday, when she had a morning tee time and started on No. 10. Sorenstam was at even par through four holes when she began a run of birdies by hitting a pitching wedge within 4 feet of the hole on the par-5 No. 14. She followed with birdie putts of 24 feet on No. 15 and 20 feet on No. 17.
She also closed with a flourish, making birdie putts from 16 feet on No. 6, 20 feet on No. 7 and 10 feet on No. 9, after which she tossed a ball to some young fans in the gallery.
Her 64 matched the second-lowest opening-round score on tour this year, and at 7-under, she's already two shots lower than her winning score last year at Cedar Ridge.
'It seemed like I rolled in everything I looked at,' Sorenstam said.
D'Alessio, who posted the best finish of her seven-year LPGA tour career when she tied for third with Hjorth in last year's tournament at Cedar Ridge, rolled in almost everything down the stretch. She posted three birdies on her final four holes, including a pair of 30-foot putts on No. 15 and No. 17.
She finished fifth two weeks ago in the Wendy's Championship for Children in Dublin, Ohio.
Ammaccapane, who's yet to break the top 20 in a tournament this year, played in the morning's opening group. She birdied four of the first five holes to take the early lead and made the turn at 3 under, then sank a 20-foot birdie putt on No. 9 to finish with a 67.
McGill, who has only one top-10 finish this year, hit every fairway and missed only one green, at No. 17, when, on what she called 'my best swing of the day,' her shot caught the fringe and kicked over the green.