Coco Gauff, of the United States, reacts during a match against Mirra Andreeva, of Russia, during the second round of the U.S. Open tennis championships, Wednesday in New York.

NEW YORK — Coco Gauff used the phrase “when I was younger” after her second-round victory at the U.S. Open on Wednesday while discussing the perspective she’s gained at the ripe old age of 19.

“I used to think,” she explained, “every match was life or death.”

And now? Well, the American said after beating 16-year-old Mirra Andreeva of Russia 6-2, 6-3 in Arthur Ashe Stadium that losses are OK “as long as you learn from them.”

Gauff is not getting much opportunity for that sort of learning lately — she’s won 13 of her past 14 contests, including claiming the two biggest titles of her still-nascent career — and yet her game has been showing a lot of growth lately.

“Obviously maturity plays a part into it. The more matches you have, the more experience you have,” said Gauff, who is seeded sixth at Flushing Meadows and on course for a potential quarterfinal showdown against defending champion Iga Swiatek, also into the third round after winning in straight sets Wednesday.

“Mirra, she’s going to be a great player,” continued Gauff, whose breakthrough came at age 15 when she qualified at Wimbledon and got to the fourth round. “With the more matches she has, the more experience she has.”

And then Gauff closed with quite a compliment: “I really see myself in her.”

The two teenagers faced each other about three months ago at the French Open in what was a much tighter affair, going three sets before Gauff — the runner-up to Swiatek at Roland Garros in 2022 — pulled out the win.

Gauff next faces 32nd-seeded Elise Mertens of Belgium, who came back to beat American Danielle Collins 3-6, 7-6 (9), 6-1.

Novak Djokovic and Swiatek rolled to straight-set victories to move into the third round, fighting not only their opponents but sticky, 85-degree Fahrenheitweather on the hottest day at the tournament so far.

“That’s why we train several hours a day in humid, hot conditions so we can be ready for whatever awaits you on court,” the second-seeded Djokovic said after a 6-4, 6-1, 6-1 victory in Arthur Ashe Stadium over 76th-ranked Bernabe Zapata Miralles of Spain.

“I still have the hunger,” said the 36-year-old from Serbia who owns 23 Grand Slam titles. “I still got it.”

Swiatek, the top-seeded defending champion from Poland, had only slightly more trouble in her 6-3, 6-4 victory over 322nd-ranked Australian Daria Saville in Louis Armstrong Stadium. Swiatek has never lost in a major to a player outside the top 100.

In the biggest upset of the day, seventh-seeded Stefanos Tsitsipas fell in the second round to 128th-ranked Swiss qualifier Dominic Stricker 7-5, 6-7 (2), 6-7 (5) 7-6 (6), 6-3.

Ending the four-hour match with a forehand winner that just caught the baseline, Stricker raised his hands and flopped on his back to celebrate his first-ever victory over a top-10 player in only his third Grand Slam appearance.

“I’m just super happy right now,” Stricker told the Grandstand crowd. “I came out and felt good from the first set on. … I just kept playing high-level tennis.”

Tsitsipas, a Grand Slam finalist at the Australian Open and French Open, has still never advanced beyond the third round at Flushing Meadows. The Greek is the second-highest seed to go down on the men’s side after No. 4 Holger Rune of Denmark lost to 63rd-ranked Spaniard Roberto Carballes Baena.

Elsewhere, Dominic Thiem, the 2020 U.S. Open champion, retired soon after dropping a first-set tiebreaker to American Ben Shelton, and French wild card Benjamin Bonzi defeated 28th-seeded Christopher Eubanks 7-6 (6), 2-6, 6-2, 7-6 (7), ending the hopes of an American who made a surprising run to the Wimbledon quarterfinals.

Fourth-seeded Elena Rybakina advanced to the third round in a walkover when Australian Ajla Tomljanovic withdrew before the match; 10th-seeded Karolina Muchova beat Magdalena Frech of Poland 6-3, 6-3; and 15th-seeded Belinda Bencic of Switzerland downed British qualifier Yuriko Lily Miyazaki 6-3, 6-3.