Joanne Morley, Becky Morgan and Michelle Estill share fourth place at 5-under-par 67.
Park, who won her first career major at this season's Kraft Nabisco Championship, was superb early in her opening round with four birdies in her first six holes. At the par-5 ninth, Park missed the fairway and was forced to lay up short of the green. She knocked a wedge on with her third, but three-putted from 50 feet.
Things did not get better for Park on the second nine. She tallied her second bogey in a row at 10 when she left her third shot in a greenside bunker.
Park rebounded at the par-5 12th when she hit a 3-wood to 30 feet with her second. She two-putted for birdie and made it back-to-back birdies with a 5-footer at 13. Park collected her third birdie in a row at 14 when she hit a sand-wedge to 7 feet. Park polished off four birdies in as many holes with a 12-footer at the par-3 15th.
Park was alone in the lead, but stumbled at 17. She hit her tee shot right and was forced to punch out into the fairway. Her third at the par-4 hole stopped 20 feet from the cup, but she missed the putt to fall to minus-5.
The tour's fourth-leading money winner in 2004 hit a 6-iron to 4 feet to set up birdie at 18 and grab the clubhouse lead.
'I'm very happy with today's round,' said Park. 'I made a couple of mental errors that cost me a few strokes, but then came back strong. I finished with birdie, so I'm pleased.'
Saiki, who won this year's Wegmans Rochester LPGA, parred her first four holes before a 6-foot birdie putt at the fifth. She made it two in a row with a two-putt from 18 feet at the par-5 sixth.
Saiki played solidly around the turn, then hit a 6-iron to 15 feet to set up birdie at the par-3 11th. She once again collected back-to-back birdies, this time with a 10-foot putt at the par-5 12th.
The 38-year-old jumped into first place at the par-5 16th. Saiki reached the front of the green with a 4-wood, then chipped in for eagle with a 9-iron from 70 feet.
'I was very patient today,' said Saiki, who almost walked away from the game earlier this year. 'But I made the putts I needed to make and chipped in for eagle.'
Cavalleri, an Italian who has yet to win on tour, opened on the back nine Thursday and collected two birdies in a row from the 13th. She parred her next six holes around the turn until a birdie at the third.
Cavalleri hit a 7-wood to 19 feet with her second shot at the par-5 sixth. She made the eagle putt, then birdied eight to join Park and Saiki in first.
'I didn't make any bogeys, which is good,' said Cavalleri. 'My putting was excellent, and the course is in good condition. It's really nice to score out here.'
Angela Stanford, Donna Andrews, Liselotte Neumann, Il Mi Chung and Heather Daly-Donofrio are tied for seventh place after opening with 4-under-par 68s.
Defending champion Rosie Jones kicked off her title defense with a 2-over-par 74 and is part of a large group tied for 92nd place.