Both competitors started off well in Italy by holding their serves and making use of the clay court with powerful and precise shots. However, it was Sharapova who managed to take control.
While Williams tried to keep the 25-year-old on her toes, Sharapova had enough composure to snatch some vital breaks and take a one-set lead in Rome.
Sharapova continued her dominance despite an edgy start to the second set, but Williams could not provide enough answers to the Russian pro's powerful shots.
The number two seed managed to grab a break of serve and keep the advantage to take the set and claim a spot in the semi-finals.