Australia’s Mack Horton has posted a personal best time to win Australia’s first Olympic gold medal in Rio.

Horton, 20, posted 3:41.55, timing the final 50m of the 400m freestyle to perfection.

Going for gold: Horton. Photo: Getty

He passed defending Olympic champion, China’s Sun Yang, to claim victory.

The commerce student from Deakin University has had fierce rivalry with Sun Yang.

Sun Yang and Horton had a run-in at training. Photo: Getty

Horton said he had no “time or respect for drug cheats” in the wake of a training run-in between the pair earlier in the week.

Fairfax Media reported that Yang had this week been taunting and splashing Horton, who ignored the gestures and continued with his training.

The report was later described by state-run Chinese media as ‘fake news’.

“I don’t know if it’s a rivalry between me and him, just a rivalry between me and athletes who have tested positive,” Horton told Channel Seven, referring to Sun’s 2014 drug ban.

Horton cruised into the final, qualifying second behind American Conor Dwyer, with Yang fourth quickest.