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.
Due to a heavy fog that never lifted off of Newport Country Club on Thursday, the plan called for 36 holes on Sunday. After the third round was completed Sunday morning, Sorenstam, Wie and Brittany Lincicome found themselves atop the leaderboard.
Sorenstam flew out of the gate in Sunday's final round with back-to-back, 4-foot birdie putts at one and two. She reached 2 under par, but Hurst also got off to a great start in the final round.
Hurst also birdied one and two, but dropped a shot at the par-3 fourth. Hurst atoned for that error with a 35-foot birdie putt at the fifth that got her to 1 under par for the championship.
Sorenstam was cruising along until the seventh. At that hole, she pulled her 7-iron approach into a creek, then had 15 feet to save bogey. That putt hit the left lip and stayed above ground. The double bogey dropped Sorenstam into a tie for the lead with Hurst and Inkster.
Inkster stopped being a factor shortly after she ended up being tied for first. She bogeyed the ninth and fell down the board throughout the final round.
The eighth became a pivotal hole. Hurst's second flew over the green and Sorenstam's second came up short of the putting surface. Sorenstam chipped to 6 feet, while Hurst chipped in for a birdie. The No. 1 player in the world missed her par putt to cap off a two-shot swing and was two behind Hurst.
Sorenstam made a complete mess of the ninth. She found a bunker and had a decent shot at par, until her putt horseshoed out of the hole. Sorenstam was now 2 over for the tournament and three off Hurst's lead.
That did not last long as Hurst missed a 9-footer at the same hole to cut her lead to two. Sorenstam cut into it even more at the 10th when she drained a 6-footer for birdie.
Hurst stumbled at 11 as she drove into the left rough. Her lie was so bad that all she could do was hit a wedge a few feet closer to the short grass. Hurst left the hole with a bogey to fall back into a tie for the lead with Sorenstam at plus-1.
At this time, Wie sank an 18-foot birdie putt at the 12th that tied her atop the leaderboard. She found a bunker at the next hole and made bogey, then never shared the lead again.
Hurst took sole possession of the lead at the 14th when she ran home an 18- foot birdie putt. Sorenstam tied her one hole later with a 15-foot birdie putt. Hurst had a closer birdie putt at the same hole that did not fall.
Sorenstam moved into first at the par-5 16th. She drove in the right rough and hit a 5-wood closer to the hole, but still in the tall stuff on the right. The Swede knocked her third to 20 feet and canned the birdie putt to move one in front at minus-1.
Sorenstam left the door open for Hurst with a bogey at 17. Hurst narrowly missed a 35-foot birdie putt at that hole, then Sorenstam did the same at 18 and now it's a Monday playoff.
'You cannot give up and I kept on grinding,' said Sorenstam. 'I'm very happy with the way I played. It's been a long week on a really tough golf course. It felt great.'
Lincicome struggled to a 7-over 78 in the final round and finished alone in seventh at plus-7. Rachel Hetherington (73) and Shi Hyun Ahn (76) tied for eighth place at 8-over-par 292.
Amateurs Amanda Blumenherst (73) and Jane Park (76) tied for 10th place with Jee Young Lee (77), Patricia Meunier-Lebouc (75), Sophie Gustafson (78) and Young Kim (74). That group came in at 9-over-par 293.