Defending champion Gauff came through an error-strewn third-round match at the China Open, saying “I did what I needed to do to win” against Fernandez.
She eventually won a tight encounter in three sets – 6-4 4-6 7-5 – but the problems with her serve that brought the American second seed to tears at the US Open resurfaced in Beijing.
The 21-year-old two-time Grand Slam champion served nine double faults and was broken seven times in the match.
Both players struggled with their serve, with 15 breaks in total throughout, including eight in the final set – three on Gauff’s serve and five on Fernandez’s.
Gauff served twice for the match from 5-2 up, only to be broken on both occasions by the Canadian world number 25, but she gathered herself at 5-5 to break straight back and finally served out the match, sealing victory on her second match point.
“It was very physical, we were going back and forth,” Gauff said in her on-court interview.
“Obviously the third set I was playing pretty well. I know I could have served a little bit better, but I did what I needed to do to win today.”
Gauff will now face either Swiss 15th seed Belinda Bencic or Australian Priscilla Hon in the last 16 of the WTA 1000 event.