Laura Davies & Lorena Ochoa share lead

The 43-year-old Davies, who won the European Tour Order of Merit for a record seventh time last year, has not won on the LPGA Tour in the United States in nearly six years.

Ochoa, meanwhile, has stamped herself a star on the US circuit, winning six tournaments last year en route to Player of the Year honors. This season she has won the Safeway International, and she is on the brink of supplanting Sorenstam as world No. 1.

Sorenstam, who has been at the head of the world rankings for six years, withdrew from the tournament on Thursday with a back injury that likely will keep her on the sidelines for at least a month.

"I have been playing with pain for quite a few weeks," Sorenstam said. "I couldn't take it much more and decided it was time to see someone after yesterday's Pro-Am."

A doctor in Florida diagnosed a ruptured and bulging disc in her back. The next step is to see a neurosurgeon in Miami.

She hopes to be back in time for the Ginn Tribute in South Carolina starting May 31. It is a new LPGA tournament, and Sorenstam is the official host.

The highlight of Davies' round - which included five birdies - was an eagle at the long third hole, where she hit a 2-iron second shot 230 yards and holed the 25-foot putt.

"I made an eagle at the third, and that got the round going," Davies said. "My only bogey was three putts at the long ninth, but it was a great way to start the tournament.

"I've been playing very consistently this season and the driver was going well today, which was the key."

With 20 US LPGA wins, Davies needs two more to get into the Hall of Fame.

"I won a tournament in Norway last year, but it would be great to win on this Tour again," she said.

Ochoa, 25, had eight birdies to sit alongside Davies.

They were one stroke ahead of American Brittany Lincicome and two shots clear of defending champion Mi Hyun Kim of South Korea. Also at 68 were American Sherri Turner and South Korean Na Ri Kim.