Annika Sorenstam, chasing a record-tying fifth straight victory, was eight strokes back to start the day and lost all hope of keeping her streak alive with three bogeys over the first eight holes on Sunday.
'I have enjoyed the ride, and it has been a dream come true,' said the Swede, who closed with a 75 to finish tied for 43rd at 4-over 220.
'After a day like today it motivates me to win.'
But Pak managed to continue another trend on Sunday. The victory, her 10th in four seasons on tour, ran the record for international players vs. Americans to 10-0 for 2001.
'Yes, Americans have not won this year, but we're all trying,' said Diaz, who recorded her second runner-up finish of the season. 'In the whole scheme of things, it doesn't really matter if you're from the U.S. or Korea or Europe. You're just going out and playing golf. We're all trying to win.'
Pak, at 7-under and one shot ahead of Michele Redman at the beginning of the final round, briefly lost the lead after her bogey at the first hole was followed by an eight-foot birdie putt by Redman at the 2nd.
Pak regained a share of the lead with a 15-footer for birdie at the 4th. Redman missed a 10-foot par putt at the 7th to drop one off the pace, then pulled alongside Pak again with birdie putt from 20 feet at the 9th.
Meanwhile Diaz, playing two groups ahead, registered her fifth birdie of the day with a two-putt at the par-5 12th to join the leaders at 7-under. Then, unbeknownst to her, Diaz was alone at the top when Pak bogeyed the 13th and Redman dropped a shot at 14.
'I don't think I was aware until the 17th hole,' said Diaz, who formerly played under her maiden name of Philo. 'I was trying not to look at the leaderboard. But there's a big one on 17 that I finally saw.'
Diaz suffered a bogey at the last hole when she failed to recover from an errant drive. She finished at 6-under 210 with a 68, one of only seven rounds in the 60s on Sunday.
'That was really incredible today,' said Diaz. 'All day, they were rooting for me. That was a great feeling. I apologize for letting them down in any way.'
Pak knocked a wedge to seven feet at 16 for a birdie that lifted her back into the lead, then sealed the win with a 12-foot birdie putt at the 17th.
'I knew I had to hang in there with the golf and I tried to play it hole by hole,' said Pak, who earned the winner's share of $120,000. 'I wanted to get the trophy, I promised myself.'
Pak, who captured two major championships as a rookie in 1998, posted her first win of the year at the season-opening YourLife Vitamins event in Orlando.
Pak led by two strokes after Thursday's first round. Play was cancelled Friday because of heavy rain and the event, which was originally scheduled to be played over four days, was shortened to 54 holes.
Redman missed the mark with a seven-foot par attempt at 17, then closed with a par for a 73 and solo third at minus 5. It was her fifth top-10 of the season and third top-five.
Denise Killeen, a member of the LPGA Tour since 1992, recorded her best ever finish Sunday, tying for fourth place at 4-under with Rosie Jones and Karen Weiss.
Rookie Becky Morgan shot the day's low round of 5-under 67 for a share of seventh place at minus 3 with Mi Hyun Kim.
Two-time defending champion Juli Inkster posted rounds of 79-68-74 this week to tie for 51st at 5-over par.
Se Ri Pak Bio
Full-field scores from the Longs Drugs Challenge