Two-time U.S. Women's Open champion Annika Sorenstam posted a 70 to move into a tie for second with one round to play. Sorenstam, who missed a birdie putt at the 18th that would have put her in the last group on Sunday with Rosales, was joined by Meg Mallon and Kelly Robbins at 4-under-par 209.
'Tomorrow I'm going to chase somebody who's playing really well,' said Sorenstam. 'I'm gonna have a lot on my mind, so it really doesn't matter which group I'm playing in. I just want to get off to a hot start.'
Rosales, the 1998 NCAA champion, was on the verge on multiple occasions before breaking through two months ago at the Chick-Fil-A Charity Championship. Now the 25-year-old has a three-shot edge and is on the brink of winning the most storied championship in women's golf.
'It didn't hit me yet,' said Rosales. 'Probably when I get to my room and settle down, probably that's when I'm going to start feeling it.'
Rosales, who carried a one-shot margin into the third round at Orchard Golf Club, stumbled out of the gate with a bogey at the opening hole to fall into a logjam at 4 under. She countered with a birdie at the par-5 third to regain the outright lead at minus-5.
At the par-4 eighth, Rosales knocked her approach to 7 feet but her birdie try rolled five feet past the hole. Rosales saved par coming back, and converted a 6-foot putt for a birdie at the ninth to make the turn at 6 under.
Rosales missed the green en route to a bogey at the 10th but hit a tremendous second shot to the par-5 13th that rolled within 7 feet of the hole. She missed the eagle putt, but tapped in for a birdie.
Rosales was steady down the stretch and played her approach to 6 feet at the par-4 16th, a hole she bogeyed on Friday. Rosales ran home the birdie try to reach 7 under, three shots clear of her closest competitors.
She almost made birdie at the 17th and sent her second shot to the top ridge on the 18th green. Rosales' birdie effort came up short, but she rolled in the par putt to secure a breathable edge heading into the final round with a few former major winners in her rearview mirror.
'I still stick to my game plane,' said Rosales. 'Birdies will come to you, you don't have to force any shots. I'm trying not to think about it too much till tomorrow, till the last hole. We'll see what happens tomorrow.'
Sorenstam had a rocky start with a pair of bogeys over her first four holes but the top player in the game responded with back-to-back birdies starting at the eighth.
The Swede dropped another shot with a bogey at the 11th. At the par-5 13th, Sorenstam hit her second shot to 12 feet and drained the eagle try to reach 4 under. Sorenstam then sank a 7-footer for a birdie at the very next hole to pull within one of the lead.
Sorenstam hit a bad approach to the 15th, however, and watched as her ball bounced through the green. She bogeyed the hole and parred her way in to finish within striking distance.
'I thought I played very sensible today,' said Sorenstam, who won this event in 1995 and 1996. 'I thought I was patient. I really didn't get off to the start I wanted, but I kept grinding, I kept trying.'
Mallon, the 1991 U.S. Women's Open, put on a putting display that included a bending, 18-foot putt at the 16th on her way to a 67, the low round of the day.
Robbins, who participated in the playoff at this event last year, was on fire early with four birdies on the front nine that gave her a share of the lead in the afternoon.
Her charge was derailed at the 10th, however, where she picked up the first of back-to-back bogeys. Robbins got one back with a birdie at the 16th to complete a round of 68.
Rachel Teske shot a 70 to finish alone in fifth place at 3-under-par 210. Michelle Ellis was one shot further back at 2-under-par 211 after a round of 72.
Michelle Wie was keeping pace with Rosales until a double-bogey at the last left her in a group at 1-under-par 212.
'It's a really great feeling, but if I was 3 under then I'd be a little bit better,' said Wie, who is playing under a special exemption this week. 'But 1-under's still pretty good in the U.S. Open.'
The 14-year-old amateur sensation mixed two birdies and three bogeys on the front nine and dropped her approach inside 6 feet for a birdie at the 11th. Wie then birdied the 13th and added a birdie at the 16th to reach 3 under.
Wie found trouble at the closing hole, however, after her second shot drifted left into the gallery. She scrambled to a double bogey to join Kim Saiki, Candie Kung, Pat Hurst and Moira Dunn in a tie for seventh.