The pair finished regulation at even-par 284 after Hurst posted a 2-under 69 and Sorenstam an even-par 71.
The duo was tied at even-par on the 18th tee and Hurst pushed her drive right. It looked like her ball was headed for a hazard, but it stayed up in a decent lie. Sorenstam split the fairway with her drive.
Hurst could not reach the putting surface with her second at 18. Sorenstam knocked her approach from 185 yards 30 feet from the flagstick. Hurst hit a solid chip shot that rolled 5 feet from the hole.
Sorenstam had a putt for her 10th major championship and second win of the year. Her ball tracked toward the hole, but eventually moved right at the last second. She left herself a tap in for par, putting the pressure squarely on Hurst's shoulders.
Hurst, the 1998 Kraft Nabisco Championship winner, holed her par save to force the first 18-hole playoff since 2003.
'I feel really comfortable over the ball,' said Hurst. 'I had a lesson on the Friday before I left for Rochester (site of last week's Wegmans LPGA). I still didn't feel very comfortable last week, but it sure came around this week.'
Michelle Wie had a share of the lead until a bogey at the 13th. She finished with a 2-over-par 73 on Sunday and a share of third place with reigning LPGA Champion Se Ri Pak (69) and Stacy Prammanasudh (72). The trio came in at 2-over-par 286.
'I still feel like I played awesome,' said Wie. 'It's just a shot here and there. I'm getting closer and closer. It's going to be very soon. I'm right there.'
Two-time winner Juli Inkster also had a piece of the lead on Sunday, but three bogeys over her final 10 holes undid her. She carded a 2-over 73 in the final round and took sixth at plus-3.