In a match between two of the tour's heaviest hitters, Williams battered Azarenka on the new blue clay court with big serves and fierce returns.
The 13-time Grand Slam winner captured the first four games and had no trouble the rest of the way.
"I can still do better," said Williams, who took a yearlong absence because of illness in 2011. "This is really good. I have been working hard. I had some tough battles and really unfortunate circumstances so I really love this."
Williams served 14 aces on her way to avenging her only loss in six previous meetings with Azarenka. She was beaten by the Belarus star in the 2009 final in Miami.
Williams won the 41st title of her career and second this season. She is unbeaten in her last 13 matches on clay. Azarenka had won her four previous tournaments.
Williams broke in Azarenka's first service game when the Australian Open winner could only stab her stinging returns into the stands. William's strong start left Azarenka shaken, and she committed three double-faults to cede her serve again and trail 3-0.
The flustered Azarenka netted a forehand after Williams had fallen on the slick surface and left the entire court open.
She then produced another double-fault to conclude a dreadful first set.
Williams kept the momentum going, hitting her fifth and sixth aces to hold for love at the start of the second set.
As her frustration boiled over, Azarenka smashed her racket to the ground moments before Williams blasted a return by her to break her yet again.
Williams sealed the victory in 64 minutes with her final ace.
"I want to congratulate Serena for a great week," Azarenka said. "She did a great job.