Gercsak made his first Hungarian team at the 2004 Summer Olympics in Athens, where he competed in the men's 4 × 200 m freestyle relay, along with his teammates Balázs Makány, Tamás Szűcs, and four-time Olympian Tamás Kerékjártó. Swimming the second leg in heat two, Gercsak recorded a split of 1:54.03, but the Hungarians rounded out the field to last place and sixteenth overall with a final time of 7:31.78.