Antyukh recorded a personal best of 52.70 to finish just 0.06 outside the Olympic record held by 2008 champion Melaine Walker, with USA's Lashinda Demus setting a season's best of 52.77 to take silver.
Czech Zuzana Hejnova claimed the bronze medal just ahead of Jamaica's Kaliese Spencer.
Antyukh said: 'I am overwhelmed with emotion. I cannot believe what has happened. I need time for it to sink in.
'I can't remember how the race unfolded. It was tough fight.'