In the junior cadet competition (under 13 years old), he defeated clubmate Uroš Vučetić in the final match with a score of 3:1.
Previously, he defeated Jakov Milošević (Lovćen) in the semifinals, while Mrkajić was better than Matija Medenica (Gorštak) 3:0.
Vučetić and Mrkajić defeated Nikola Miković (Novi) and Marko Medenica (Gorštak) 3:0 in the men's doubles final.
In the semifinals, they won against Matija Mitrić (Spin) and Damir Jašarević (Budim) 3:1, while Miković and Medenica were better than the brothers Jakov and Jovan Milošević (Lovćen) 3:2.