Djokovic admitted the truth immediately after his victory over the Vietnamese-American player at the 2025 US Open.

"I started very well," the seventh seed said. "Just over 20 minutes into the first set, I felt fine. But then, entering the long games at the start of the second set, I began feeling very bad – I don’t know why. I was truly surprised by my fitness level at that moment. We had some tight rallies, but at the same time, I lost my form, made many unforced errors, and allowed him back into the match."

"I'm happy I managed to regain my rhythm after the second set. In the third set, things were fairly steady to finish the match. The positive is I will have two days off, but honestly, I’m still a bit concerned. I’m not injured, just finding it very hard to sustain stamina during long rallies and recover after each point."

This was Djokovic's first match since his defeat to Jannik Sinner in the Wimbledon semifinals. He started energetically against an opponent nearly 20 years younger. Learner Tien – who made a splash by reaching the fourth round of the Australian Open earlier this year – demonstrated impressive skill by gradually balancing the game with strong baseline shots in the second set.

Even golf star Rory McIlroy was present to watch these intense exchanges. Tien won many long rallies and even forced Djokovic to save three consecutive break points when trailing 0-40 on serve at 2-3. The 18-year-old, coached by former Roland Garros champion Michael Chang, also created a set point opportunity at 5-4. However, Djokovic rescued it with a precise ace. Had Tien succeeded, the match might have taken a different direction.

Djokovic then surged in the tiebreak and quickly regained control in the third set despite losing a break. With this victory, he became the first player in the Open Era to win 75 consecutive first-round matches in Grand Slam tournaments.