Coco Gauff survived a shaky serving performance to battle past Ajla Tomljanović in the first round of the US Open, winning 6-4, 6-7 (2), 7-5 after 2hr 57min on Tuesday night.
"It was a tough match. Ajla was tough, she was getting so many balls back," 2023 US Open champion Gauff said.
"It wasn't the best but I'm happy to get through to the next round."
Gauff, the reigning French Open champion, had prepared for the US Open by shaking up her coaching team on the eve of the tournament in an effort to fix her shaky service game, replacing coach Matt Daly with Gavin MacMillan, a biomechanics specialist.
However, on the evidence of Tuesday night, the 21-year-old American still has plenty to work on if she is to have any realistic chance of mounting a deep run in New York.
Gauff finished with a whopping 59 unforced errors and 10 double faults, was broken six times and heads to the second round knowing that a more ruthless opponent than Tomljanovic might have punished those mistakes.
As it was, Tomljanovic had her own problems, suffering eight breaks of serve and making 56 unforced errors before bowing out.
Gauff admitted that her unsettled build-up to the tournament had been draining.
"Honestly, it's been really tough, mentally exhausting," Gauff said. "But I'm trying. It wasn't the best today, but it was an improvement on last week (in Cincinnati); I'm just trying to improve with each match."
Explaining her decision to change her coaching team so close to the start of the tournament, she said she had wanted to move quickly to take advantage of MacMillan's availability.
"I know when I did this, I was not going to maybe serve the best," Gauff said. "I just felt like I don't want to waste any more time.
"If I could have worked with Gavin earlier, I would have, but he was on the team of another player. Then he magically became available.
"I knew I had to make a quick decision because I knew he would be pretty sought after. I think hopefully this time next year I'll be serving much better."
Gauff will face Croatia's Donna Vekic in the next round.
