Deicmans ruru eru maka ihe omume igwu mmiri abụọ na 2004 Summer Olympics na Athens, site na eclipsing FINA B-ọkọlọtọ ntinye oge nke 2:03.77 (200 m onye medley) si FINA World Championships na Barcelona na 4:28.44 (400 m onye medley) si European Championships
na Madrid. Na 400 m onye ọ bụla, Deicmans metụrụ Miguel Molina nke Philippines aka iji mebie ihe mgbochi nke 4:30 ma weghara ebe nke asaa na okpomọkụ nke abụọ site na sekọnd anọ, na oge 4:29.17. N'asọmpi 200 m n'otu n'otu, Deicmans gbara ndị ọzọ na-egwu mmiri asaa na okpomọkụ nke anọ, gụnyere ndị mmeri Olimpik ugboro abụọ Jeremy Knowles nke Bahamas na Ioannis Kokkodis nke Gris. Ọ gara n'ọkwa nke ise site na 0.39 nke abụọ n'azụ Barbados' Bradley Ally, na-agbaji ndekọ Latvian nke 2:03.68. Deicmans enweghị ike ịga n'ihu na ọkara ikpeazu, ebe ọ bụ na ọ nọ na nke iri abụọ na ise n'ozuzu na preliminaries.