Cristie Kerr is alone in second place at 5-under-par 65. Liselotte Neumann, Grace Park, Catriona Matthew and last week's State Farm Classic winner Patricia Meunier-Lebouc share third place at minus 4.
Hanson broke into red figures early Friday with a 14-foot birdie putt at No. 1. She added a four-foot birdie at the par-5 third and collected another birdie at the eighth when she laced a 5-iron to four feet.
Hanson continued her fine form on the back nine when she landed an 8-iron three feet from the hole to set up birdie at 11. She knocked a seven-iron to 12 feet for birdie at 15 and made it back-to-back birdies with a 20-footer at the par-5 16th.
She ran into trouble at the 18th after her ball fell against the lip of a greenside bunker. Hanson hit a soft pitch out of the trap to save par and keep the first-round lead to herself.
'I've been working on my bunker play this week,' said Hanson, who is winless in seven years on the LPGA Tour. 'I saw exactly where I needed to hit it and I put it right there.
'I hit my driver well so it's much easier to hit it closer to the pins from the fairways than the rough and that is the first key. The second key is I did hit some good iron shots. I was able to attack the pins and I felt good with my putter.'
Kerr recorded two early birdies with a pair of five-footers at three and four, but her play around the turn moved her up the leaderboard.
She drained a 25-foot birdie putt at the seventh and knocked a 4-iron inches from the hole for a tap-in birdie at the 194-yard ninth. Kerr's run continued on the back nine when she holed a 15-foot birdie at 10 and an eight-footer at the 11th.
Kerr, who will make her Solheim Cup debut for the American team in two weeks, ran into trouble at the 18th. She pushed her drive right and missed her second right of the green. Kerr's pitch landed 10 feet from the hole and she two-putted for bogey, dropping out of the lead.
'I am a little upset at the last hole,' said Kerr, who won for the first time on tour at the Long Drugs Challenge in April. 'I mean I'm happy with the way I was hitting the ball, executing and thinking.'
Annika Sorenstam, playing for the first time on the LPGA Tour since missing the cut at the Women's British Open, posted a 2-under 68. She is tied for seventh with Maggie Will and Kris Tschetter.
Se Ri Pak, a three-time winner on tour in 2002, struggled to a 5-over-par 75 and is tied for 105th.
Gloria Park, who won this event in 2001, opened her title defense with a 2-over 72 and shares 49th place.
Full-field scores from the Williams Championship