The 29-year-old American, gunning for her second title of the season following her triumph in Montreal, will take on Russian Veronika Kudermetova on Sunday.
The pair traded breaks early in the second set before Pegula stepped up the pressure again, firing a sizzling forehand winner en route to a 4-2 lead.
Pegula finished the job when she forced Sakkari into making a mistake from the back of the court.
Earlier, Kudermetova outlasted former French Open runner-up Anastasia Pavlyuchenkova 7-6(6) 6-7(2) 6-3 in a gruelling battle lasting three hours and 25 minutes to make her second final of the season.
"But today I'm really happy that I managed to win the match and to be in the final."
Persons:
Jessica Pegula, Greece's Maria Sakkari, Androniki, Maria Sakkari, gunning, Russian Veronika Kudermetova, Pegula, Sakkari, Kudermetova, Anastasia Pavlyuchenkova, Roland Garros, Shrivathsa Sridhar, William Mallard
Organizations:
Pan, Ariake, Greece's Maria Sakkari REUTERS, Rights, Pan Pacific, Thomson
Locations:
Tokyo, Japan, United, Montreal, Russian, Guadalajara, Bengaluru