'It's a wonderful day,' said Sorenstam, who won for the 54th time on the LPGA Tour. 'I'm very pleased with the way I played today. To win this championship again means a lot to me.'
Park, who held the lead after each of previous three rounds, was fighting hard to stay in control at Bighorn Golf Club until some costly mistakes on the back nine opened the door for Sorenstam. Park carded a 1-over 73 to take second place at 15-under-par 273. Lorena Ochoa was two shots further back at 13-under-par 275.
Sorenstam was three behind Park to start the day and managed a lone birdie on the front side to continue to lurk. The back nine was a different story as the Swede began her climb up the leaderboard with a two-putt birdie at the par-5 12th.
'It seemed like all day Grace had a nice little lead,' Sorenstam said. 'I felt like I had a lot of chances, but really didn't make anything. Then I got a little extra adrenalin pumping.'
At the par-5 15th, Sorenstam missed the green with her second shot, but chipped in for eagle to join Park in the lead at 17 under. While Park was falling apart on the closing holes, Sorenstam hit her approach to 6 feet at the par-4 17th and drained the birdie putt to take the outright lead.
Park had gotten it to 18 under with a birdie at the 12th, but she missed the green at the par-3 13th and was unable to get up and down en route to a bogey.
The Korean found trouble again at the 17th after her second shot missed the putting surface. She played her third to 6 feet, but missed the putt to fall two shots behind Sorenstam.
Park needed to hole out on the closing hole, but was unable to do so, granting the win to Sorenstam.
Park, who has a strong record when carrying a lead into the final round on the LPGA Tour, had a rocky front nine with a bogey at the second. She recovered with a birdie at the following hole, but a double bogey at the par-4 fourth dropped her back to minus-14.
She regained her composure with back-to-back birdies from the seventh and hit her second shot to 8 feet for a birdie at the par-4 11th. Park then birdied the 12th and was seemingly on the way to her sixth career victory on the LPGA Tour, but when she started to drop shots down the stretch, Sorenstam seized the opportunity for her fourth victory at this event.
'This is special to come from behind,' said Sorenstam, who earned her sixth victory of the season. 'I played really well today.'
On the other side was Park, who had to deal with the disappointment.
'I fell apart and didn't get it done, and that's it,' she said. 'I missed a few shots in the beginning, but just couldn't get the job done.'
Last year's winner Sophie Gustafson posted a 1-under 71 to finish alone in fourth place at 11-under-par 277. Cristie Kerr followed at 10-under-par 278 after a round of 75.
Juli Inkster and Jeong Jang shared sixth place at 9-under-par 279 while Karen Stupples and Shi Hyun Han were one shot further back at 8-under-par 280.
Amateur sensation Michelle Wie continued her fine play on the weekend with a 2-under 70 to finish at 5-under-par 283 along with Jennifer Rosales.