Serena Williams of the US returns the ball to Anna-Lena Friedsam of Germany during their second round match for the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 10 May 2016. EPA/ETTORE FERRARI

Serena Williams of the US serves the ball to Anna-Lena Friedsam of Germany during their second round match for the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 10 May 2016. EPA/ETTORE FERRARI

Serena Williams of the US returns the ball to Anna-Lena Friedsam of Germany during their second round match for the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 10 May 2016. EPA/ETTORE FERRARI

Serena Williams of the US reacts during the second round match against Anna-Lena Friedsam of Germany in the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 10 May 2016. EPA/ETTORE FERRARI

Serena Williams (L) of the US reacts during the second round match against Anna-Lena Friedsam of Germany in the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 10 May 2016. EPA/ETTORE FERRARI

Serena Williams of the US returns the ball to Anna-Lena Friedsam of Germany during their second round match for the Italian Open tennis tournament at the Foro Italico in Rome, Italy, 10 May 2016. EPA/ETTORE FERRARI