The 19th-ranked Elise Mertens beat the fourth-ranked Gauff 6-3 6-3 to reach the Beijing quarter-finals on Wednesday.
In Monday's match against home player Sun Xinran, Gauff stopped a rally after electronic advertising boards lining the court flickered during a point late in the first set.
Sun appeared about to win the point when Gauff stopped playing. The chair umpire then ordered a replay of the point, which Gauff won.
"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."
"There is no place for racism, discrimination, or abuse in tennis," the WTA told Reuters in a statement.
"We are appalled by the racial abuse directed at Coco Gauff and are in contact with her to offer our full support.
"As we do for all WTA players experiencing online abuse, our Threat Matrix team is monitoring the abusive messages, working with the athlete's team to report them to the relevant platforms and seeking action on the content and the accounts responsible."
The Threat Matrix service was launched in 2024 and uses AI and open-source data to help protect athletes from online abuse and harassment.
Gauff's challenge unravelled amid a barrage of errors, with the 2024 Beijing champion committing 34 unforced errors, including eight double faults, during the 78-minute defeat in which she dropped her serve four times.
Mertens reached her first quarter-final at a WTA 1000 event - the level just below grand slams - in five years.
She now faces six-time grand slam champion. The Pole broke Iva Jovic's serve twice in the last four games to beat the 18-year-old 6-1, 6-3.
In other matches Qinwen Zheng defeated Alina Charaeva 6-1 2-6 6-4 to become the only unseeded player into the quarter-finals. There she will meet Ukrainian sixth-seed Elina Svitolina, who brushed aside Ann Li 6-2 6-3.
