Speaking to the media after beating Sun by a mere .16 of a second to win the 400m freestyle gold , Mack Horton described his win as one "for the good guys."
Prior to the race, Horton said Sun, who served a three-month ban for testing positive for a banned substance in 2014, was a "drug cheat."
Australia's chef de mission Kitty Chiller flatly ruled out any chance of an apology on Tuesday, according to CNN affiliate Sky News Australia
Speaking to reporters, she said Horton "has every right to express his views and his displeasure."
"We have no intention of making an apology," she added.
The spat adds another dimension to the men's 1500m freestyle race on Friday, when Sun and Horton will face off again. Sun won gold in the 200m freestyle on Monday.
'Don't cry Sun'
The Australian's comments sparked fury in China after an emotional Sun broke down in the post-race press conference, accusing Horton of deliberately trying to psych him out.
A hashtag "Sun Yang Don't Cry" quickly went viral on the Chinese web, and Horton's Facebook, Twitter and Instagram posts were flooded with comments attacking him and demanding he apologize to Sun.
"You are too complacent and will die quickly," read a comment on one of Horton's Instagram posts. Others called him a "loser" and "shameful," and flooded the comments with the snake emoji.
Chinese state media also joined in the outrage. An op-ed
published by the nationalistic tabloid Global Times described Australia as a country "at the fringes of civilization" and referred to its history as "Britain's offshore prison."
Horton "couldn't hold in his cynical smugness after beating Sun, and the Australian media recklessly spread Horton's rude speech," the op-ed said.
Sorry not sorry
Speaking to state-run news agency Xinhua
, Chinese swim team manager Xu Qi said Horton's "inappropriate words greatly hurt the feelings between Chinese and Australian swimmers."
"We strongly demand an apology from this swimmer," Xu added.
Meanwhile, Australian medalists also backed Horton, according to Sky, including gold medalist trap shooter Catherine Skinner and the bronze medalist diving pair Maddison Keeney and Annabelle Smith.
"I'm all for clean sport. Everyone should have an equal playing field," Keeney said. "I support Mack. I'm with him all the way."
Global Times hit back immediately
, saying in an official editorial that, while it was unsurprising that the Australians were unwilling to discipline a recent gold medalist, the affair demonstrated the Australian Olympic committee's "swaggering ego."
"Horton and his backers represent the dark side of Australian society, and it is time for us to look at the bright side of the Olympic Games," the editorial said. "This trifling botheration won't ruin our beautiful memories of this grand event."