Chinese sports fans and local media have turned on Australia's newest Olympic swimming sensation Mack Horton, accusing the 20-year-old of "taunting" home favourite Sun Yang by calling him a "drug cheat" to his face in a post-race press conference.

Horton had already raised the stakes in the electrifying rivalry between the two swimmers before their 400-metre freestyle final, saying he had "no time or respect for drug cheats", referring to Sun's three-month doping ban in 2014. He then backed up his talk with a nerveless swim to hold off a fast-finishing Sun, clinching Australia's first gold at the Rio Olympics.

Footage of a devastated Sun bursting into tears while attempting to give an interview in the media mixed zone immediately after the race went swiftly viral on Chinese social media. The top-trending hashtag "Sun Yang Don't Cry" amassed more than 47 million views on China's Twitter-like Weibo within hours.

DOMINIC EBENBICHLER/REUTERS Australian Mack Horton qualified second-fastest for the 400m freestyle final on day one at Rio.

But as well as sympathy and support for their fallen champion, there was much vitriol directed at Horton. Fans on social media as well as reports on popular Chinese online news portals including Sina and Tencent described the Australian's "drug cheat" comments as classless "taunts", and for rubbing it in after winning. The anger is only likely to intensify as news filters through that Horton has since conceded it was part of a deliberate ploy to unsettle his rival.

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DOMINIC EBENBICHLER/REUTERS Controversial Chinese swimmer Sun Yang has been making waves at the Olympic training pool.

After the rivals failed to acknowledge each other in the pool immediately after the race, they shared a sporting handshake for the cameras during the medal ceremony. But the truce was short-lived after Horton, responding to questions from Chinese journalists and while sitting right next to Sun, repeated his views in the post-race press conference.

"I used the word 'drug cheat' because he tested positive," Horton told reporters. "I just have a problem with him testing positive and still competing."

Sun responded by accusing Horton of playing mindgames: "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."

Official state-run media in China have been slower to report on the spat between Sun and Horton, with their swimmer's doping past a sensitive topic. In their live coverage, state broadcaster China Central Television focused on their swimmer's valiant effort in defeat and expressed hope he could regroup for his next event, the 200-metre freestyle.

Sun tested positive for the stimulant trimetazidine at the Chinese national championships in 2014, but the Chinese Swimming Association attracted controversy for quietly handing down a three-month suspension which expired in time for him to compete in the Asian Games later that year. The ban only came to light when announced by international swimming body FINA, months after the fact.

Sun has said previously the substance was contained in heart medication he was using and that it did not enhance his performance.

"For doping cases I don't understand why the media pay so much attention to this," he said at the time. "Around the world when China has good results people always think something bad. We are training as hard as all athletes in other countries."

The Horton-Sun showdown made for more unhappy viewing for Chinese sports fans in Australia, who were already fuming after Channel Seven cut to a commercial break just as the Chinese team entered the Maracana stadium during the network's live coverage of the opening ceremony on Saturday. The network then attracted further anger and ridicule on Chinese social media after using Chile's flag, instead of China's, in a projected medal tally graphic.

It sets the scene for another hotly-anticipated Australia-China rivalry in the pool, with Cameron McEvoy and Ning Zetao the two favourites for the blue-ribbon 100-metre freestyle. The hugely popular Ning is currently arguably China's biggest sports star, while McEvoy enjoys a cult following in China after he won plaudits for applauding Ning after coming second to him in last year's World Championships.

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