Serena Williams is back.

Ending an eight-month layoff, Williams easily won her opening match Friday at the NASDAQ-100 Open, beating qualifier Marta Marrero 6-1, 6-0.

The match was the first for Williams since she earned her sixth Grand Slam title by beating older sister Venus at Wimbledon last July. She had been out since undergoing knee surgery Aug. 1 but showed few signs of rust.

Williams' first stroke was a service winner, and she won eight of the first nine points with little effort. She closed each set with an ace, displaying the same overpowering game that had her ranked No. 1 before she was sidelined.

"I definitely was a little nervous," she said. "But once I stepped on the court, I was OK."

The victory was the 13th in a row at Key Biscayne for Williams, a two-time defending champion. Marrero offered little resistance, winning just 23 of 74 points and double-faulting eight times.