Rio De Janeiro: Mack Horton has backed up the talk to walk the walk, winning Australia's first gold medal of the Rio Olympic Games with a stirring victory in the 400m freestyle final over arch-rival Sun Yang.

Horton swam a tactically perfect race before holding off Yang in a ding-dong battle over the final lap, just hours after declaring the former Chinese doper a cheat for whom he had neither time nor respect.

Champion: Mack Horton shows off his gold medal. Credit:Joe Armao

It was a massive call to go on the offensive before a big final but the 20-year-old never looked nervous, holding his form to touch the wall in 3:41.55 and earn the first of what should be a golden night for Australia in the pool.

The performance was hailed as a victory for clean athletes over drug cheats, although Horton was magnanimous enough to initiate a handshake with Yang as he stood atop the podium to collect his gold medal and hear the Australian anthem.