The daughter of Mexican immigrants, Salas was introduced to the game when her father, the head mechanic at Azusa Greens west of Los Angeles, did some handyman jobs for the club pro and, instead of pay, asked him to teach his daughter to play.
She went on to star at Southern California, where she was a four-time All-America selection and helped the Trojans win the 2008 NCAA title.
The victory came on a rare weekend when her parents didn't come to the tournament, but watched from their home in California, and it brought tears to the eyes of Hall of Famer Nancy Lopez, who has been a mentor of sorts for Salas.
"I'm crying. I'm so proud of her," Lopez said by telephone after watching the celebration on the green. "She looked great out there, just very confident and swinging great. ... Like she said on TV, she was ready. It was time."
Salas expects "some tears of happiness" when she sees her parents Monday.
Tseng, seeking her first victory since 2012, got within three with three birdies in a four-hole stretch on the back nine, but she finished with two pars and a double bogey for a 69, expanding Salas' lead to five shots.
Thompson had a 69, and Smith shot 66 — the best round of the day.
Tseng nearly made it very interesting at the par-5 15th, but her eagle putt stopped just short of the cup.
"One more roll it will be in," she said. "I know if I make that I have a good chance."
The tournament also featured a golf rarity, a double eagle. It was scored by Frenchwoman Joanna Klatten on No. 15.
Klatten said her drive left her a perfect distance away for her 3-wood, and she had a feeling something great was coming.
"It's intuition. I had a good feeling about that shot," she said. "Of course there is a little bit of luck in that."