Gauff stopped a rally after electronic advertising boards lining the court flickered during a point late in the first set of her 7-5 6-1 third-round victory over Sun, a 16-year-old who recently won the US Open junior title.
"Hey everyone, you can dislike me or disagree about what happened without being racist," Gauff, who is Black, said in a reply on X.
"The amount of racist comments/dms I've received in the last few hours is insane. Lastly, I'm not a cheater or a thief."
Sun appeared about to win the point when Gauff stopped playing. The chair umpire then ordered the point to be replayed.
Gauff, a two-time grand slam champion ranked No.4, went on to take control of the match on Monday.
"Xinran is (an) incredible talent and player, I apologized for the situation at the end of the match and she completely understood," Gauff added in another post.
Sun, who was given a wild-card entry by tournament organisers and was making her WTA Tour debut, appeared distraught after the loss.
Gauff, who reached the fourth-round of Wimbledon as a 15-year-old in 2019, sympathised with Sun.
"I did not like to see her so emotional as I've been there and I really understand what it is like but this is just the beginning of an incredible career," Gauff said.
"It was an honor to share the court in front of her home crowd."
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