Park made a 20-foot putt on the par-4 18th to sweep the first two LPGA majors of the season. She rebounded in the playoff after blowing a three-shot lead with a closing 3-over 75. The top-ranked South Korean star bogeyed three of the final five holes in regulation and hit only six fairways in the round.
''It feels great. It was a tough day out there,'' Park said. ''The amount of fairways I was missing today, it's almost a miracle that I won today. I think I got a little lucky there, too. And I really tried to fight off and tried not to give up. That really paid off.''
The 42-year-old Matthew, from Scotland, shot a bogey-free 68 to match Park at 5-under 283 at Locust Hill.
It was a dramatic finish to a marathon of a day in which organizers were forced to squeeze in the final two rounds after torrential rain postponed the first round Thursday.
And a 36-hole day ended up going 39. The tournament wasn't decided until nearly 8 p.m. ET, some 12 hours after Matthew teed off to open her third round.
''I felt like I ran a marathon today,'' Park said. ''I'm just happy we got it done. A major championship should have this kind of challenge, not the 36 holes every time, but this golf course.''
After both made par on the first two playoff holes, Matthew struggled off the 18th tee on the third. After having difficulty advancing the ball out of the rough just below the green on her third shot, Matthew missed a 50-foot par chip.
''I don't think fatigue was a factor during the playoff,'' Matthew said. ''I think just the adrenaline of being in the playoff kept you going. I certainly didn't feel tired during the playoff.''
The 24-year-old Park also won the Kraft Nabisco in California in early April and has four victories this year. With the victory, Asian players have won nine straight majors.
Also the 2008 U.S. Women's Open winner, Park became only the seventh player to win the LPGA's first two majors in a season, and the first since Annika Sorenstam won the same two events in 2005.
Park has seven career LPGA victories, six in her last 22 starts.
In claiming the $337,500 first prize, Park increased her season winnings to $1.22 million, and moved into 25th on the LPGA's career list at just under $6.5 million.
Suzann Pettersen and Morgan Pressel tied for third, a shot behind the leaders. Pettersen had the low round for the tournament, closing with a 65. Pressel collapsed after she opened the day with a two-stroke lead through two rounds at 6-under 138.
Park lost her rhythm and focus through the final round. She hit only six of 14 fairways and only eight of 18 greens in regulation in the fourth round.
Frustrated with her play, Park said it wasn't until the playoff began when she was able to refocus.
''Nothing seemed to be working. I really cleared my head, and just looked at the fairway and just smashed it,'' Park said, referring to teeing off at 18, the first playoff hole. ''I should've done that before and I wouldn't have to play three more holes.''
Trailing Pressel by five shots midway through the third round, Park surged into a one-shot lead with birdies on four of her final six holes for a 68. Despite her struggles, it was a lead she wouldn't relinquish.
After shooting 71 in the third round, Pressel had a 75 in the final round.
Park spent the final two rounds playing in the final threesome with Pressel and Chella Choi.
Tied with Pressel at 7 under with nine holes left, Park appeared to take control in building a three-shot lead after the 12th hole.
Pressel bogeyed Nos. 10 and 12, while Park drained a 3-foot putt for a birdie on No. 11.
Park, however, couldn't close, and had to scramble to make a bogey on the 18th.
She flew her tee shot into the left rough, and barely advanced the ball with her second shot.
Park carried the green with her third shot, which landed in the rough about 25 feet above the hole. Park putted to within 16 inches on her par attempt, before sinking it for a bogey.
''I pretty much played against Morgan all 36 holes. I was just trying to play better than her today,'' Park said, before noting she was surprised there was another contender. ''I didn't know she was up there until I was I was on No. 18.''
Matthew's day took a surprising turn, as well.
Playing in the third-to-last threesome, Matthew opened the day at 2-under 142, four shots behind then leader Morgan Pressel. And Matthew then fell further back after shooting a 73 in the third round.
The 18-year Tour veteran, however, persevered, with a bogey-free round of 68. Her final birdie came on the par-5 17th hole, which at that time put her one shot behind Park, who was in the process of shooting a bogey-5 on the 16th hole.
Matthew then spent the final few holes staying loose on the putting green.
''When I started the last round, I probably didn't realize I could win,'' she said. ''So to play well, and get into the playoffs was obviously pretty good. Obviously, when you get into it, it's pretty disappointing. But overall, a pretty good week.''
At least the weather finally cooperated after persistent rain spent much of the past three days water-logging the 6,500-yard course. Though several fairways and greens were still soggy, the players at least had the benefit of playing under mostly sunny skies and with temperatures pushing 80.