Stefanos Tsitsipas threw his racket in the air, walking to the net with the sort of smile he was uncertain would ever surface again. 

Just one year ago, the two-time Grand Slam finalist left Flushing Meadows in fear, unable to walk for two days due to a back injury that made him question whether his career could continue.

Tsitsipas, 28, spent months in physical agony, as the once-perennial top 10 player watched his ranking plummet, wondering why he continued to push himself through so much pain. 

“It was tough,” Tsitsipas said, choking back tears after his U.S. Open first-round match Monday. “It was something that I never really experienced before … I remember saying to my team, ‘I don’t know for how long that’s going to continue.’

“I stayed strong. I kept believing. I knew deep inside that I will have a moment again.”

Tsitsipas, who debuted at the U.S. Open in 2018, walked into Louis Armstrong Stadium as an unseeded player in New York for the first time in his career, having fallen to his lowest ranking (No. 88) in more than eight years this summer.

Despite falling down a set and a break against No. 10 Arthur Fils — who had just won the Cincinnati Open — Tsitsipas walked out with a 4-6, 7-6 (3), 6-1, 6-4 upset, defeating the Frenchman for the first time in six matches.

“I am speechless,” Tsitsipas said after the win. “It’s very easy to not feel confident, especially when you haven’t beaten top players in a long time. That’s why I’m very ecstatic about today. It’s one of those moments that you are able to look back and be, like, I’ve still got the game that I’m looking for.”

Injuries and internal battles were only partly responsible for Tsitsipas’ slide.

After an early exit at Wimbledon — the ninth straight Grand Slam in which he failed to advance past the second round — Tsitsipas fired his father, Apostolos, as his longtime coach, following years of public conflict.

Now, the former world No. 3 is working with Thomas Perrin and Patrick Mouratoglou, the latter best known for his partnership with Serena Williams.

“I personally felt like I needed it,” Tsitsipas said. “I needed a different voice. I needed someone that provides a little bit more calm into my tennis world. There was a lot of chaos surrounding me before and a lot of noise. It took a long time to figure it out and realize that I just can’t cope with it anymore.

“I also realized [the importance of] having people that sometimes bring the best out of you instead of the worst version out of you, these are some of the things that need fixing.”

Despite a hard-court résumé that includes one final appearance and three other semifinal runs at the Australian Open, Tsitsipas has long struggled in Queens, having never advanced past the third round despite being a top 11 seed on six occasions.

In his past five appearances at the U.S. Open, Tsitsipas was knocked off by unseeded players.

Now, he is one, free from expectations, believing his best days may still be ahead. 

“Why not?” he said.