Williams, who lost only one set in the tournament, defeated Sharapova 6-1, 6-4. Williams is 13-2 all-time versus Sharapova, including a championship match win earlier this year in Miami.
The result kept Sharapova, No. 2 in the rankings, from regaining the No. 1 spot in the rankings.
Sunday marked the 12th consecutive meeting with Sharapova won by Williams. Sharapova hasn't beaten Williams since the finals of the WTA Tour Championships in 2004.
Williams established control of the match with a first-set in which she lost only four points on serve and finished in three of her five break opportunities.
Sharapova opened the second with a break -- her only break of the day -- but Williams evened the set at 3-3 with a break at love and finished the match with a backhand winner down the line that completed another break at love.
The win was the 50th WTA title for Williams, which is the most among active players and sixth all-time. Williams is 50-16 in finals, having won 15 of the last 17 tournament she reached the title match.
Sharapova slipped to 29-21 in finals. She is 2-2 in championship matches this year.