Williams did not lose a set during the event and finished off Cirstea 6-2, 6-0 to win for the 42nd time in her last 43 matches. Her lone setback in that span came in the fourth round at Wimbledon, where she was surprised by Sabine Lasicki.
Other than the Rogers Cup title, the world's top-ranked player has tournament wins this year in Australia, Qatar, Spain, Italy and two in the United States. She also won the French Open, her only triumph among the three major championships played thus far in 2013.
Williams recorded the 54th tournament victory of her career, moving her past Monica Seles into ninth place on the all-time list. Another victory will put Williams in a tie with Lindsey Davenport and Virginia Wade for seventh place.
This was the third career meeting between the Rogers Cup finalists and Cirstea has won just seven games in those matches. Williams defeated Cirstea in the third round of the French Open this year.