The 20-year-old coped better with the windy conditions in California than the Greek, claiming the decisive one of the seven breaks of serve in the first set.
She went 3-1 up in the second to set up a win that will lift her to a career-high second in the world rankings.
“Today was pretty crazy because of the conditions,” Swiatek said.
The victory was Swiatek’s 11th in a row in a year where she reached the Australian Open semi-finals before lifting the title in Doha last month.
“After playing so well at previous tournaments, I didn’t know if it was possible for me to play that well and that long,” the 2020 French Open champion said after winning the fifth WTA title of her career.