NEW YORK (AP) — Daniil Medvedev had an easy start to his U.S. Open title defense, beating Stefan Kozlov 6-2, 6-4, 6-0 on Monday.

Simona Halep had another early exit, this one coming in a memorable first tour-level win for Ukrainian Daria Snigur.

Snigur upset the No. 7 seed 6-2, 0-6, 6-4, then struggled through tears to explain what the victory meant to her family and her country, which is at war with Russia.

On the same Arthur Ashe Stadium court where Serena Williams began what could be the final tournament of her career with a 6-3, 6-3 victory over Danka Kovinic on Monday night, the top-seeded Medvedev looked just as strong as he did in sweeping past Novak Djokovic in last year’s final for his first major title.

Medvedev advanced to face Arthur Rinderknech of France. The Russian is trying to become the first repeat champion at the U.S. Open since Roger Federer won five straight from 2004-08.

“I need to be at my best on Wednesday and I’m going to try to make it,” Medvedev said.

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Andy Murray was another early winner, 10 years after winning the first of his three Grand Slam titles in Flushing Meadows. He had one of the first upsets of the tournament by beating No. 24 seed Francisco Cerundolo of Argentina 7-5, 6-3, 6-3.

“It seems like a long time ago,” Murray said of his victory over Djokovic in 2012. “A lot’s happened since then in my career.”

Djokovic couldn’t travel to the tournament this year because he isn’t vaccinated against COVID-19.

Fourth-seeded Stefanos Tsitsipas won’t be staying in it after dropping the first 11 games to qualifier Daniel Elahi Galan before falling 6-0, 6-1, 3-6, 7-5.

Many fans arriving for the day session at the final Grand Slam event of the season were focused on the match that would lead off the action at night. Williams, the 23-time major champion, has said she is preparing to end her tennis career.

Coco Gauff wasn’t going to miss it, saying she was going to change plans and attend instead of watching on TV in her hotel room.

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“As I thought about it, I was, like, I have to watch,” the 18-year-old American said after her straight-sets victory. “I’m excited and, you know, it’s not often we watch live matches, to be honest.”

Last year’s women’s finalist, Leylah Fernandez, and this year’s Wimbledon runner-up, Nick Kyrgios, were winners in night matches, with the Australian saying he watched Williams’ ceremony on TV before following her onto the court.

They faced more comfortable conditions after a hot start under a sunny sky in Flushing Meadows. Leading 3-0 in the third set, Medvedev told the chair umpire he wanted a bag of ice so he could put it on his head.

“It was pretty hot today and humid,” Medvedev said. “I see the other guys coming from five-setters in the locker room, pretty red faces. That’s also fun in a way sometimes to get through these conditions. Even today, the match was maybe not that intensive and long, but, yeah, I sweated a lot and it was not easy.”

Taylor Fritz, the No. 10 seed, said he he struggled with the windy conditions in his four-set loss to qualifier Brandon Holt, the son of two-time U.S. Open women’s champion Tracy Austin.

Snigur was playing her first match in the main draw of a Grand Slam. The 20-year-old wore a ribbon in the blue and yellow colors of Ukraine’s flag on her chest, and she put her hands around it after finishing off the victory.

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She played last week in the “Tennis Plays for Peace Exhibition” to raise money to aid Ukraine. That was on Louis Armstrong Stadium, which may have calmed her nerves a bit when she was sent back out onto the same court Monday.

“I think it helped me because I was here in ‘Tennis Plays for Peace’ and I think it helped me a little bit,” Snigur said as she fought through tears during an on-court interview.

Halep had won 19 of her last 22 matches and recently returned to the top 10, but the U.S. Open has been the most challenging major for the two-time Grand Slam champion. She is 21-11 in New York and has lost in the first round of three of her last five appearances.

Bianca Andreescu, the 2019 U.S. Open champion, needed three sets to get past Harmony Tan, the French player who beat Williams in the first round at Wimbledon.

Two other past champions had short stays. Dominic Thiem, the 2020 champion who missed last year because of injury, fell to Pablo Carreño Busta in four sets. The 2016 winner, Stan Wawrinka, retired from his match against Corentin Moutet after losing a second-set tiebreaker. He has been plagued by injuries in recent years.

No. 29 seed Tommy Paul overcame the heat to outlast Bernabe Zapata Miralles 4-6, 6-3, 2-6, 6-0, 7-5 in 3 hours, 10 minutes. Fellow American Sebastian Korda also got his first win at his home Slam, beating Facundo Bagnis in four sets.

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Another American advanced in an upset, with J.J. Wolf ousting No. 16 seed Roberto Bautista Agut in straight sets.

Also, Wu Yibing became the first Chinese man to win a U.S. Open match in the professional era, upsetting No. 31 seed Nikoloz Basilashvili 6-3, 6-4, 6-0. He had played his way into the field through the qualifying tournament, joining countryman and fellow qualifier Zhang Zhizhen as the first Chinese men in the U.S. Open main draw since the open era began in 1968.

Zhang lost his first-round match.

Third-seeded Maria Sakkari and No. 17 Caroline Garcia were among the early winners on the women’s side, with Sakkari overcoming Wimbledon semifinalist Tatjana Maria in three sets.

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