[3][4] Dashdavaa made his official debut for the 2004 Summer Olympics in Athens, where he competed for the men's half-lightweight class (66 kg).

He defeated Greece's Giorgi Vazagashvili in the first preliminary round, before losing out his next match, by an ippon (full point) and a tomoe nage (circle throw), to Japan's Masato Uchishiba.

Dashdavaa also qualified for the repechage rounds, but lost again by an ippon and a kuchiki taoshi (single leg takedown) to Argentina's Jorge Lencina.

He defeated United States' Ryan Reser and Poland's Krzysztof Wiłkomirski in the preliminary rounds, before losing out the quarterfinal match, by an ippon and an uchi mata (inner thigh throw), to Iran's Ali Maloumat.

Unfortunately, he finished only in ninth place, after losing out the second repechage bout to Japan's Yusuke Kanamaru, who successfully scored a waza-ari (half-point) and an o goshi (full hip throw), at the end of the five-minute period.