MACK Horton, the kid who looks like Clark Kent and swims like Superman, is being hammered by Chinese online trolls after labelling their hero Sun Yang a 'drug cheat'.

Horton, who delivered Australia's first gold medal of the Games, has not been afraid to call out the Chinese star after he served a three month suspension in 2014 when he tested positive to a banned substance.

Horton, who wear 5.75 prescription goggles in the pool,  edged out Sun Yang in the men's 400 metres freestyle final, swimming his race perfectly to out-touch the defending Olympic champion.

It didn't take long for the trolls to target him.

"Your pathetic "victory" is built on calumny, ignorance and smear! SHAME ON U!!!! #apologizetosunyang,'' one wrote.

There's no love between the two swimmers.

The Chinese swimmer splashed water in the face of the Victorian during a training session at the Olympic aquatic centre earlier in the week.

At the time Horton said Yang "splashed me to say hello, and I didn't respond because I don't have time for drug cheats".

After the thrilling race, Horton said he "didn't have a choice" but to beat Yang.

"The last 50 metres I was thinking about what I said and what would happen if he gets me here," he said.

"I used the words drug cheat because he tested positive ... I just have a problem with athletes who have tested positive and are still competing."

Yang has denied he is a drug cheat.

"I don't care too much what the Australian athlete says ... I'm clean; I've done everything it takes to prove I'm clean," he said.

He accused Horton of playing mind games.

"On the competition stage, every athlete deserves to be respected and there's no need to use these sort of cheap tricks to affect each other."

The Independent reported that Yang burst into tears while attempting to give an interview in the media mixed zone after the race, footage of which went swiftly viral on Chinese social media.

Within hours, the hashtag "Sun Yang Don't Cry" amassed more than 47 million views on China's Twitter-like Weibo.

Chinese fans have slammed Horton for his comments.

"Your parents and whole country should be shame [sic] on what you've said," one user wrote on Instagram.

Another wrote: "You even won the match, but you are still a loser, you don't deserve to have an Olympic gold medal."

Many other spammed Horton's accounts with snake emojis.