Mantzaris's debut with the senior national team at the 2014 FIBA Basketball World Cup was a triumph of his perseverance, as he had torn the ACL in his right knee at the start of 2013 and remained side-lined until the start of the following season. He returned to action however with the same determination and the same spirit of self-sacrifice which have earned him a well-deserved reputation as the elite Greek perimeter lock-down defender. The point guard has also shown great improvement in his shooting over the past year while he has always been an excellent passer with an innate organising ability, especially in half-court play. Mantzaris helped Greece step on the podium in four consecutive youth championships within only three years, from 2008 through 2010. His older brother, Antonios, is also a basketball player and was an international with the U18 and U20 national teams.