Coco Gauff said she had been left drained by the racist abuse she experienced during the China Open after losing in the last 16 to Elise Mertens.

The American was dismayed earlier this week after an incident during her match against Chinese teenager Sun Xinran. The 16-year-old thought she had hit a winner late in the first set but Gauff had raised her hand to stop the point because she was distracted by flickering lights on the stadium’s advertising hoardings. The move prompted some boos from the crowd. The umpire agreed to have the point replayed, and Gauff went on to win 7-5, 6-1.

On social media, Gauff called out the “insane” amount of racist messages she had received after the match, adding: “I’m not a cheater or a thief.”

Gauff also clarified that she challenged the point before Sun had returned the ball, when she noticed the lights flicker for a second time.

Asked about the incident, a spokesperson for the Women’s Tennis Association said it was “appalled by the racial abuse directed at Coco Gauff and are in contact with her to offer our full support”.

Gauff was far from her best on Wednesday against Mertens, hitting eight double faults and 34 unforced errors overall in a 6-3, 6-3 defeat.

Gauff, who has an excellent record in China, was asked by reporters in Beijing whether she had been affected by the abuse.

“It has been kind of draining, I’m not going to lie. I just turn off my phone and move on. There’s nothing you can do,” she said. “I think today I was just a bit flat. I just didn’t play well. I think I wasn’t moving well. There were a lot of things I didn’t do well.”

During the match, she told her ​team that she had “no ​energy” and felt as though she might pass out.

“I ​think I just ‌didn’t play well,” ​Gauff said. “I think ​I wasn’t moving well. There were a lot of things I didn’t do well. I thought Elise played well on the big points, made me play a big ball, yeah.”

Mertens will face Iga Swiatek in the quarter-finals after the eighth seed defeated American Iva Jovic 6-1, 6-3.