Williams, No. 1 in the world, piled up six breaks, including one in the next-to-last game. She put the match away by holding serve at love to improve to 12-2 lifetime versus Azarenka, who is third in the rankings.
Williams will be the clear favorite going into the French Open, which begins May 26, with Sunday's win marking her 32nd win in her last 33 matches on clay courts over the last two years. She also ran her current winning streak to a personal-record 24 matches.
Four of Williams' breaks came in the first set when she won 60 percent of the points. The only game she lost in the set came on a break.
Azarenka got a second break in the match that got her back on serve in the second set but Williams powered her way to the win, winning 60 percent of the points on serve overall and 57 percent off Azarenka's.
The Italian Open was the 51st career championship for Williams, which is sixth most all-time. Azarenka is 16-12 in WTA title matches. Sunday snapped a personal four-match final winning streak for Azarenka.