The 3-2 victory over FC Girondins de Bordeaux in a semi-final tie saw Strasbourg reach the final for the first time in 14 years.
Mothiba grabbed two second half goals which helped Le Racing secure victory at the Stade de la Meinau in the city of Strasbourg.
The win set up a tie with Bafana Bafana international Lebogang Phiri's En Avant de Guingamp in the final of the Coupe de la Ligue which is also known as the League Cup.
The final is scheduled to take place at the Stade Pierre-Mauroy in the city of Villeneuve d'Ascq on the 30th of March 2019.
Guingamp booked their place in the final after stunning AS Monaco in the semi-finals.