Maria Hjorth and Sarah Lee share second place one stroke further back at minus-7. Michele Redman posted a 6-under-par 66. She was joined in a tie for fourth place by Michelle Ellis, Young Kim and Jean Bartholomew.
Women's world No. 1 and defending champion Annika Sorenstam birdied two of her last three holes to post a 3-under-par 69, where she is tied for 28th.
Sorenstam, a three-time winner of this event, started on the back nine and opened with a birdie on No. 10. After a bogey on 12, she birdied 13 and 15. The Swede tumbled back to even-par with bogeys on 16 and 17.
The 35-year-old made the turn at minus-1 thanks to a birdie on the 18th. Sorenstam parred the first six holes of the front side before birdies on seven and nine put her at 3 under on the Prospector Course at Superstition Mountain Golf and Country Club.
'Today was a tough round. It was kind of a roller coaster,' admitted Sorenstam. 'I had some really good shots and then I had some bad ones. I have a few things to work on, but I'm very happy with 3 under, it could have been worse.'
Song got off to a fast start with birdies at two and three. She moved to minus-3 with a birdie on the sixth. The Thailand native made it two straight as she also birdied the seventh.
The 19-year-old made the turn at 5 under after a birdie on the ninth. Song birdied 10 to get within one of Lee's lead. Song drained her third birdie in a row at 11 to join Lee at minus-7.
Song parred four straight holes from the 12th. She birdied the 16th to take the lead. Song, who won the 1999 U.S. Girls's Junior amateur to become the youngest winner in event history, closed with back-to-back pars.
'Well everything went as planned today pretty much,' Song said. 'I hit a lot of fairways and a lot of greens and made some really good putts. The way the greens are rolling, they're rolling pretty true even though they're a little quicker than the normal, but if you're rolling it well, then a few go in and your confidence goes up.'
Lee opened on the 10th tee and bogeyed each of her first two holes. She got those strokes right back with birdies on 12 and 13. Lee got into red figures with a birdie on No. 15.
The 27-year-old jumped to 3 under with a hole-in-one at the par-3 17th.
'Yes, that was my first hole-in-one, believe it or not,' said Lee of her 6-iron shot. 'Actually, I missed the shot a little right. So it got a lucky, lucky bounce.'
Lee kept soaring as she birdied 18 and No. 1 to get to 5 under. After five pars in a row, Lee birdied the seventh and eighth to move to 7 under.
'In the morning, it was a really chilly day. I tried, but I couldn't even warm up,' Lee said. 'I didn't hit it great early, but just stayed focused and positive.'
Hjorth got off to a flying start with birdies on four of her first five holes. The Swede continued her streaky play with three straight pars, then consecutive birdies from the ninth.
The 32-year-old stumbled to her lone bogey on the 12th. Hjorth, a two-time winner in the 1999 season, birdied No. 14 to get back to minus-5. She birdied the next as well to share second place.
Paula Creamer, the 20005 Rookie of the Year, opened with a 5-under-par 67. She shares eighth place with her 2005 Solheim Cup teammate Meg Mallon, as well as 2004 Women's British Open winner Karen Stupples, Brooke Tull, three-time LPGA Tour winner Lorena Ochoa, Mikaela Parmlid, Kate Golden, five-time tour winner Mi Hyun Kim and 2003 Kraft Nabisco champion Patricia Meunier-Lebouc.