At the 1976 European Indoor Championships in Munich Bratanov won gold in the men's 400 metres, setting a new Bulgarian indoor record of 47.79 in the final to defeat West Germany's defending champion Hermann Köhler. Bratanov set his personal best in the 400 m hurdles, 49.77, in Fürth on 13 June 1976; he was the first Bulgarian to break 50 seconds. He made his Olympic debut in Montreal later that summer, running 51.84 in the heats and 50.11 in the semi-finals; he qualified for the Olympic final, in which he placed sixth in 50.03.