Park had two eagles and five birdies and was at 18-under 198 at the Sunrise Golf and Country Club.
"Today, probably, was almost perfect for me," Park said. "I hit the ball great and putted really good today. Couldn't ask for better weather. It was a perfect day. The conditions of the golf course were perfect. I was able to go at every pin, so I was able to play aggressive."
Suzann Pettersen of Norway had six birdies in a round of 66 to sit in second place, two shots ahead of defending champion and local favorite Yani Tseng (66).
"I feel like I left lots of birdie chances out there today," Tseng said. "I didn't putt well again today, and I just feel (I'm) very (much) struggling out there."
Catriona Matthew of Scotland had a 68 and was in fourth, another two shots back at 12-under 204. Christie Kerr (67) of the United States was at 10 under.
More Sports Headlines
Snohomish mixed martial artist returns to her first love Mariners beat Twins 4-3 in 11 innings Charles scores 29 points, Liberty beat Storm 78-62 4:49 p.m. Park wins Women's British Open, captures 4th different major 4:38 p.m. Perry wins 2nd straight Champions Tour's 3M Championship 4:33 p.m. Merritt shoots 67 to win Quicken Loans National by 3 shots 4:30 p.m. Triple Crown winner American Pharoah wins $1.75 million Haskell Invitational Bills' Ryan names Incognito starting left guard
Our new comment system is not supported in IE 7. Please upgrade your browser here.