Antonov qualified for two swimming events at the 2004 Summer Olympics in Athens, by eclipsing FINA B-standard entry times of 23.48 (50 m freestyle) and 51.65 (100 m freestyle) from the Missouri State Swimming Championships. In the 100 m freestyle, Antonov challenged seven other swimmers on the fourth heat, including two-time Olympians George Gleason of the Virgin Islands and Allen Ong of Malaysia. He rounded out the field to last place and fifty-second overall by 0.29 of a second behind Ong in 52.33. In his second event, 50 m freestyle, Antonov matched his position from his first on the morning's prelims. Swimming in heat five, he touched out Iceland's Örn Arnarson to take a sixth spot by 0.17 of a second, outside his entry time of 23.67.