Muguruza won the opening set and was in control of the second before former world number one Azarenka retired due to a leg injury, the score 6-1 3-1 at the time.
The victory handed Muguruza her maiden trophy of the season and seventh of her career, while it marked the first time she has defended a title.
Two-time grand slam champion Azarenka was making her first appearance in a WTA decider since returning to the Tour following the birth of her son in December 2016.
Not since March 2016 had Azarenka – plagued by off-court and fitness issues – featured in a singles final and it did not go according to plan on Sunday.
The first-set scoreline was lopsided but Azarenka was not without her chances, having squandered a 0-40 opportunity on Muguruza's serve in the fourth game.
Azarenka – the fifth seed – wasted another three break points as Muguruza held for a commanding 5-1 lead before closing out the set.
The end was in sight early in the second set after Azarenka received treatment during a medical timeout – the Belarusian eventually calling time on her title tilt following 66 minutes of play.