It was Pak's fifth career victory at the tournament. She closed with a 4-under-par 67 to end at 17-under 267.
"Basically, this was a lovely week for me," she said. "I was really happy I was able to come back."
Pak claimed a winner's check of $195,000 for her 24th tour victory.
Pressel (68), who made a hole-in-one at the par-3 sixth, bogeyed the 72nd and final hole to finish 14-under 270.
She was the Kraft Nabisco champion earlier this summer.
At the pivotal sixth, Pak remained steady after Pressel's ace with her fourth straight birdie at the same hole. She fended off all challenges from that point.