Serena Williams opens clay season with routine win in Rome

Williams finished with 28 winners to Peterson's eight, and committed only two more unforced errors than the 58th-ranked Swede, 22-20.

Williams was playing for the first time since withdrawing ahead of her third-round match in Miami because of a left knee injury. The last time Williams played in Rome was in 2016 when she won the last of her four Italian Open trophies.

"I haven't been able to train or practice a lot. I was out much longer than I expected," Williams said. "But I did everything I could to stay fit and to keep my cardio up. I knew that I love the clay season and I wanted to be a part of it."