The American has now won back-to-back WTA clay titles after claiming Charleston in the US a month ago.
“I’m so happy to win this title,” said Williams, who now owns five wins on the clay. “I really felt good on the court.”
The bruising victory lifted the American to a 7-1 record over Azarenka, who won her only match in the series in Miami, 2009.
Williams swept to a double-break in 12 minutes at the start, secured the set in 26 minutes on a double-fault and continued the demolition in the second set to complete the win in 64 minutes.
Williams has now won 13 consecutive clay matches including the Fed Cup in April.
With the Rome Masters beckoning on Monday, Azarenka maintained a positive attitude.
“Serena played well and I didn’t today,” said the Belarusian. “She was so much better than me.
“But I have to take the positives. These moments let you see what you can do better. I know I can come up with better things the next time – and I will.”
She added: “I had a few opportunities in the second set with break points but I didn’t take anything today. I tried to get back into the match as much as I could but it didn’t work.”