NEW YORK — Coco Gauff overcame some uneven serving early in the second round of the US Open before stretching her winning streak to nine matches at the site of her first Grand Slam title with a 6-4, 6-0 victory over 99th-ranked Tatjana Maria on Wednesday night.

“I can serve better,” Gauff said. “That first set would have been a lot easier.”

Gauff, a 20-year-old from Florida, had all sorts of trouble at the outset under the lights at a hot and muggy Arthur Ashe Stadium against Maria, a 37-year-old from Germany who made it to the Wimbledon semifinals two years ago and hits slices on nearly every forehand and backhand.

“At first, last week, I felt more pressure,” Gauff said about coming back to Flushing Meadows as the defending champion, speaking during an on-court interview conducted by 2022 Wimbledon runner-up Nick Kyrgios. “But now, stepping on the court, I really have nothing to lose … and I have the potential to do more, whether it happens this year or in the future.”

There were seven double faults for Gauff in the initial set. She put in fewer than half of her first serves. She faced five break points but saved four. And problems arose in other aspects of her play, too, including winning the point on just 9 of 17 trips to the net, and a total of twice as many unforced errors, 20, as winners, 10.

Her body language frequently seemed negative after some of her mistakes. Gauff would look at her guest box and put her palms up as if to say, “What is going on?” She would roll her eyes or put a hand on a hip, including after one wild swinging volley that sailed several feet long.

When Gauff served for the opening set, she double-faulted twice and faced a pair of break points that would have allowed Maria to get the score to 5-all. But Maria missed a forehand on the first, and Gauff struck a cross-court forehand passing shot on the second, then finished off the game.

The second set was a completely different story.

Gauff put together 15 winners to merely five unforced errors — two of which were double faults — and went 10-for-11 at the net.

“I should have done that more in the first,” the No. 3-seeded Gauff said about her success when moving forward.

On Friday, she’ll take on 27th-seeded Elina Svitolina, a three-time major semifinalist who was a 6-1, 6-2 winner against Anhelina Kalinina, for a berth in the fourth round.

Gauff arrived in New York off a series of early exits elsewhere. That included two consecutive losses at hard-court tuneup events this month, which followed eliminations in the fourth round at Wimbledon and the third round of the Paris Olympics, both in July.

“It’s been a tough few weeks,” Gauff said.

Gauff’s nine double faults Wednesday were three more than she had in her opening-round match against Varvara Gracheva. She put only 43% of her first serves in play Wednesday, way down from the 64% mark in her opening match.

Despite the serve troubles, Gauff closed out both her first- and second-round matches with a 6-0 set. She is the first defending US Open women’s champion to win two bagel sets in her first two matches since Serena Williams in 2013 (won title).

Gauff also improved to 22-3 in majors since the start of her 2023 US Open title run. That’s the most major wins by any woman in that span.

ESPN Stats & Information and The Associated Press contributed to this report.