Sorenstam, 1-3 against Hetherington in LPGA Tour playoffs, won the 16th with a par when the Australian made a double-bogey 6, then hit her tee shot within 3 feet on the par-3 17th to set up a conceded birdie that ended the match.
``I thought Rachel played really well,'' Sorenstam said. ``I'm excited about the way I played. ... Today is a beautiful day. Perfect to play golf in.''
The Swedish star used a 6-iron on the 168-yard 17th.
``She gave me 16, then I had a good yardage and a good club on 17,'' Sorenstam said.
Sorenstam faced Candie Kung in the afternoon quarterfinals on the hilly Highlands Course. The eighth-seeded Kung beat No. 56 A.J. Eathorne 4 and 3.
Sorenstam, who needed a 30-foot birdie putt to finish off Tina Barrett in 21 holes on Friday, is still having trouble adjusting to the rain-slowed greens a week after tying for 23rd in the U.S. Women's Open on Cherry Hills' fast putting surfaces.
``They're still quite slow,'' Sorenstam said.
After halving five straight holes, Hetherington hit her second shot on the 16th into the right bunker and needed two shots to get the ball on the green.
``I missed the shot right on 16 and that's what it came down to,'' Hetherington said. ``I hit the ball pretty solid and was putting well.''
Sorenstam won the par-4 sixth and eighth holes with birdies to take a two-hole lead, but Hetherington countered with birdies on the par-5 ninth and par-4 10th to square it. Sorenstam missed a 4 1/2-foot birdie putt on No. 9.
Karrie Webb and 60th-seeded Marisa Baena also advanced in the upper bracket.
Webb, the slumping Hall of Famer seeded 29th, beat No. 13 Jeong Jang 4 and 2 a day after knocking out No. 4 Paula Creamer.
``It's hard to say that you're cruising, but it was nice to not to have to go to 18 again,'' Webb said.
Baena beat No. 21 Jennifer Rosales in 20 holes, birdieing the par-5 second to win after squaring the match with birdies on Nos. 14 and 17. Baena opened with a victory over No. 5 Natalie Gulbis and beat major champion Grace Park on Friday.
In the lower bracket, 14th-seeded Wendy Ward beat No. 30 Christina Kim 1-up with a birdie on No. 18 to set up a quarterfinal match against No. 59 Sophie Gustafson, a 1-up winner over Japanese star Ai Miyazato.
No. 39 Pat Hurst and No. 47 Meena Lee also advanced. Hurst beat Nicole Perrot in 22 holes, and Lee eliminated Liselotte Neumann 3 and 2.