"Today she had another great serving day against me," said Sharapova, who never had a break point.
Williams finished the tournament without dropping a set. She also beat Azarenka in round-robin play, one of her four wins against the No. 1 player this year.
"If I'm playing well and doing everything right, it's pretty difficult to beat me, without trying to sound too full of myself," Williams said. "And I hate to lose."
She has won 12 straight against opponents ranked No. 1 or No. 2 and has not lost to a player ranked in the top 2 since 2007.
Williams was not her mighty self early in the year following injuries and illness. Shortly after winning Wimbledon two years ago, she cut her foot on glass at a restaurant, leading to a series of health problems, including hospitalization for blood clots in her lungs. She also injured her ankle at the start of the year in Brisbane, Australia.
Williams last finished the year as No. 1 in 2009. She has held the No. 1 ranking for 123 weeks.