[2] Lesun started out his sporting career as a swimmer, before switching to modern pentathlon at the very young age.

[5] Following his triumph, Lesun qualified for the 2012 Summer Olympics in London, along with Moiseev, to compete in the men's event, which included a first-ever combined running and shooting segment.

[3] During the competition, Lesun made a strong showing in the fencing segment, tying in second place with China's Cao Zhongrong for a score of twenty-five victories, but struggled to maintain his position in the entire event, with disappointing scores in freestyle swimming and horse riding.

At the combined running and shooting discipline, Lesun progressed into the event in third place, until he was surpassed by Hungary's Ádám Marosi to win the bronze medal, dropping him out of the podium to a fourth-place finish, with a score of 5,764 points.

[7] At the 2017 World Modern Pentathlon Championships in Cairo, Egypt, Lesun suffered a back injury in the fencing segment, leaving him without a medal in the individual competition.