	The Derby was run on 19 May and Cossack started 5/1 second favourite behind Conyngham on 5/2 in a field of thirty-two runners, the largest ever assembled for the race. Even by the usual standards, the crowd was immense, with a "countless multitude" arriving via the newly opened Epsom railway station. After the police had cleared the spectators from the course, the race began with a clean start. Ridden by Sim Templeman, Cossack was second in the early stages, but moved into the lead by half way and soon opened up a clear advantage and was being cheered by the crowd as the likely winner half a mile from the finish. He was still three lengths in front in the straight and the only challenge came from War Eagle who moved almost level in the final furlong before being "shaken off". Cossack won easily by a length from War Eagle, with Van Tromp, who had been badly hampered early in the race, a further four lengths back in third. The value of the race was £5,250. At Royal Ascot in June, Cossack was allowed to walk over for the Swinley Stakes, when the other runners where withdrawn.