Saiki, who had four runner-up finishes between 1996-98, had never held the lead entering the final round prior to this event. Things got tight down the stretch, but Saiki rallied with two late birdies to earn her first win and $225,000.
'It really hasn't sunken in yet. I think tomorrow I'll feel it and be a little more emotional about it,' Saiki said.
Mi Hyun Kim and Rosie Jones, who won here in 1991 and 1998, shared second place at 10-under-par 278. Brandie Burton fired a 6-under 66 to come in fourth at 8-under-par 280, with Jeong Jang and Patricia Meunier-Lebouc one stroke further back at minus-7.
The 28-year-old Saiki birdied the par-4 first to get to minus-14, but stumbled to a double bogey at the very next hole. She then settled in to par nine straight holes at Locust Hill Country Club.
'After the birdie on the first hole, the adrenalin was unbelievable,' said Saiki. 'I got up to the second hole and I just hit a drive straight right and really had no play, but after I doubled that hole, I was still very calm.'
Saiki came back with a birdie at the par-4 12th to get back to minus-13. She tripped to a bogey at the very next hole, but erased that mistake at the par-4 14th.
Saiki, an All-American at the University of Southern California, parred the 15th and 16th, while her foes dropped off the pace. She closed at minus-14 with a birdie at the par-5 17th to secure her first crown.
'I've always believed in myself,' said Saiki, a 13-year professional. 'I mean I wouldn't be out here if I didn't think that I could win. I mean every week that I tee it up, I believe I can win a golf tournament. In the past when I finished second, I just got out-played. I didn't play poorly, I just got out- played, so I've always believed I could win.'
Jones tried to put pressure on Saiki, but struggled mightily on the back nine. She picked up two birdies and a bogey on the front nine to get to minus-13.
Around the turn, she bogeyed the 11th and faltered to a double bogey at the par-4 14th. She came back with a birdie at the 15th, but tripped at the 16th to finish four strokes off the pace.
Kim rose up the leaderboard with three birdies and one bogey on the front nine. She picked up another birdie to go along with eight pars on the back nine to share second place.
Annika Sorenstam, who has never won here, closed with a 1-over 73. She shared seventh place at 6-under-par 282 with Laura Davies, Candie Kung, Paula Marti and Suzann Pettersen. Catriona Matthew finish one stroke further back at minus-5.
Amateur Paula Creamer, who shared second place last week, finished alone in 13th place at 4-under-par 284. Rachel Teske, the 2003 champion, paced a group of six players one shot further back at minus-3.