The German's 56-minute knock out came two days after she was confirmed at the top of the WTA rankings, displacing Serena Williams after making it to the third round at last week's Madrid Open.
The defeat demonstrated more of the patchy and inconsistent form which the 29-year-old cannot seem to shake since starting to duel with Williams at the top of the WTA listings last season.
She lost serve five times to join another drawcard at the Foro Italico Maris Sharapova on the sidelines.
Meanwhile, Rafael Nadal advanced to the Rome Masters third round as fellow Spaniard Nicolas Almagro was forced to retire with a left knee injury.
Almagro, a three-time French Open quarter-finalist – he lost all three to Nadal – was unable to continue after 24 minutes while trailing his compatriot 3-0 in the first set.