Laura Diaz carded a final-round 67 to tie for third with Iben Tinning, Janice Moodie and overnight leader Catriona Matthew at minus-eight.
Pak took the lead in the tournament for the first time at the 17th hole. She dropped a three-foot birdie putt at the 400-yard hole and then drove into the rough on the right side at Sunningdale's closing hole.
Pak comments on her third major
She was able to play a 7-iron to four feet, which set up birdie on No. 18, but she had to wait as five groups behind her had to finish.
'There was nothing to lose and I was trying to go for it,' said Pak, who only needs the Nabisco Championship to round out the career Grand Slam. 'It was the last day and the last chance for me. I just played and played. I thought that if I finished the last three holes perfect I'd be in good shape.'
Karrie Webb, looking for her third major title of the 2001 campaign, struggled on Sunday with a 2-over 74. She bogeyed three consecutive holes on her front nine and never was a factor on Sunday.
Pak got her round started with an eagle-three at the first hole but parred the remaining holes on the front side. She made birdie at No. 10 and added another two holes later to get into the hunt.
Diaz birdied her first six holes on Sunday to move to the top of the leaderboard before the last groups even teed off. She birdied No. 10 but bogeyed Nos. 14 and 16 to fall into a share of third.
Matthew began the round with a pair of birdies but negated them with back-to-back bogeys at Nos. 5 and 6. She bogeyed two of her last four to fail in her attempt at a first major on the LPGA Tour.
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