Swiatek wrote her name in the history books when she became the lowest-ranked woman to win the French Open the previous year at rank 54.
On the back of her early Rome exit, Serena is set to continue her clay preparation at Emilia Romagna Open in Parma, Italy.
In a lopsided final, the Polish star did not lose a single game against the 2019 Rome champion to wrap up the match in just 46 minutes.
Pliskova will play reigning Roland Garros champion Iga Swiatek for the title in Rome.
Barty overcomes Tamara Zidansek in three sets, while Swiatek eases past Laura Siegemund in straight sets.
Victoria Azarenka will not play the Stuttgart Open as she will receive her first coronavirus vaccine shots.