The Pole, back from injury and gearing up for her French Open title defence next month, and world number two Sabalenka traded powerful baseline blows before Swiatek earned a second breakpoint at 4-3.
She whipped a superb forehand down the line to go 5-3 up before easily holding serve to clinch the first set on her second set point.
Swiatek, fit again following a rib injury that forced her to withdraw ahead of the Miami Open and Billie Jean King Cup qualifiers after she hurt herself during her run to the Indian Wells semi-finals last month, broke her opponent again in the first game of the second set.
Belarusian Sabalenka started to pile up unforced errors and struggled with her serve at 2-0 before firing a cross-court forehand to hold.
However, she could not break Swiatek back and the Pole held serve at 5-4 to seal her second title of the year.
"I want to thank my team because it has been such an intense time. I am so happy we are making the right decisions," Swiatek said, following her well-timed return from injury.
"It is a pretty exciting time. I will be coming back because I love this tournament."
She's now even more heavily fancied to win her third French Open and fourth Grand Slam at Roland Garros in June.
