Zatsepin qualified for two swimming events at the 2004 Summer Olympics in Athens, by clearing a FINA A-standard entry time of 2:02.15 (200 m individual medley) from the Russian Championships in Moscow. He also teamed up with Maksim Kuznetsov, Yevgeniy Natsvin, and Stepan Ganzey in the 4×200 m freestyle relay. Swimming the second leg, Zatsepin recorded a split of 1:51.75, and the Russian team finished the heats in eleventh overall with a final time of 7:23.97.