Stefanos Tsitsipas of Greece outlasted Andy Murray of Britain in a five-set U.S. Open first-round thriller 2-6, 7-6 (9/7), 3-6, 6-3, 6-4 on Monday at Arthur Ashe Stadium.

Murray, 34, is ranked No. 112 in the world and has earned 46 titles over the span of his career, while Tsitsipas, 23, is ranked No. 3 in the world and the winner of seven titles.

"Physically, I've been good since I've been here in the matches," Murray said before the start of the U.S. Open. "I pulled up well the following days after them. That for me has been really positive. I would obviously like my game to be in a better place."

"It didn't come easy," Tsitsipas said. "Lots of sacrifices I had to make on the court to get back."

Two-time Grand Slam champion Simona Halep, battling back from injury, advanced to the second round of the U.S. Open on Monday as the hardcourts showdown began before full-capacity crowds.

The 29-year-old Romanian 12th seed defeated Italy's Camila Giorgi 6-4, 7-6 (7/3) to book a second-round match against Slovakian Kristina Kucova, who ousted American Ann Li 7-5, 6-1.

Halep, the 2018 French Open and 2019 Wimbledon champion, tore a left calf muscle at the Italian Open, missed the French Open and Wimbledon, then suffered a right thigh injury at Cincinnati, but made a solid New York start.

2017 champion Sloane Stephens edged Madison Keys 6-3, 1-6, 7-6 (7) in a rematch of their final four years ago.

Former finalist Kevin Anderson of South Africa fired down 49 aces to defeat Czech Jiri Vesely 7-6(1) 4-6 3-6 7-6(5) 7-6(4) in the first round on Monday, stunning spectators at the U.S. Open.

Anderson rattled off 17 aces in the final set alone, the last one coming on match point. Then he broke into wide grin in his moment of triumph before hoisting his arms aloft.

While his ace tally was well short of John Isner's record of 113, which he achieved during his 11-hour five-minute first-round win at Wimbledon in 2010, it nonetheless earned a standing ovation from the crowd packed into one of Flushing Meadows' outside courts.

Anderson, the runner-up in 2017, faces 11th seed Diego Schwartzman of Argentina in the second round.

Former champion Marin Cilic of Croatia retired from his first-round match against German Philipp Kohlschreiber on Monday with an apparent injury, his earliest exit from the U.S. Open in 13 attempts.

The 2014 winner had been up two sets but bowed out of the match early on in the fifth, with Kohlschreiber leading 2-0, after struggling with his serve.

It was Cilic's first retirement in more than 800 matches on the tour and the first time he had failed to make it past the opening round at Flushing Meadows, as he joined American John Isner as one of the higher-profile players to exit the tournament on Monday.

Carla Suarez Navarro of Spain received a standing ovation at Flushing Meadows on Monday after the fan favorite brought down the curtains on her Grand Slam singles career following her first-round loss at the U.S. Open.

The 32-year-old Spaniard announced in September 2020 that she was being treated for early-stage Hodgkin lymphoma and underwent several months of grueling chemotherapy and radiotherapy before returning at the French Open in June.

The former world number six, who is known for her sublime single-handed backhand, had already announced she would be making her last Grand Slam singles appearance in New York.

"I lost, but this year was a gift," Suarez Navarro said after her 6-2 6-4 loss to Danielle Collins of the United States.

"Last year on these dates, I didn't know if I could be here one more time or not, and I'm here," said the Spaniard, who had been in hospital on this date a year ago. "I'm happy for that."

Suarez Navarro, who twice made the quarter-finals in Flushing Meadows, said she is proud of what she's achieved in the game.

(With input from agencies)