Bratanov equalled the Bulgarian record in the 400 m hurdles (51.8) in 1971; in 1972, he won the Bulgarian championship for the first time and improved the national record to 51.24. He repeated as national champion in 1973 and 1974; at the 1974 European Championships in Rome he was eliminated in the semi-finals, but set a new Bulgarian record of 50.66. In 1975 Bratanov won bronze at the European Indoor Championships in Katowice as the Bulgarian team's anchor in the 4 × 2 laps relay.