Despite a straight-sets victory, Djokovic wasn't entirely dominant, facing several challenging games against his 19-year-old opponent. In the second set, the former world number one committed 20 unforced errors. At times, Djokovic struggled physically, even under favorable evening playing conditions.

Djokovic reaches for a shot during his victory over Tien in the first round of the US Open at Arthur Ashe Stadium, New York on 24/8. Photo: Reuters

Djokovic reaches for a shot during his victory over Tien in the first round of the US Open at Arthur Ashe Stadium, New York on 24/8. Photo: Reuters

Djokovic's difficulties stemmed from Tien's determined comeback in the second set. After quickly losing the first set in 20 minutes, the Vietnamese-American rallied, pushing the second set to a tie-break and only succumbing after an 80-minute battle. It was an impressive set from Tien, currently ranked 50th by the ATP, who has already secured four victories against top-10 players this year.

Tien nearly won the second set, reaching set point in the 10th game. However, serving, Djokovic became more assertive, saving the crucial point before defeating his younger opponent 7-3 in the tie-break. Tien's consistent baseline play proved effective against the older Djokovic, whose movement seemed less agile than usual. Earlier in the set, the Grand Slam record holder fell while returning a serve, seemingly affecting his subsequent movement.

Tien's biggest weakness was exposed against Djokovic, committing five double faults in the first two sets. Facing one of history's best returners, Tien attempted to place his second serves in difficult positions. However, this proved a double-edged sword, disrupting his rhythm and frequently forcing him to save games. In the third set, despite capitalizing on an early break point in the first game, the 19-year-old lost all four of his service games, unable to save any break points. Djokovic also showed some inconsistency in this set but still won after 36 minutes.

"The second set was the turning point for me; if I hadn't won it, things would have been very difficult," Djokovic admitted in his post-match interview. "We played contrasting sets, and fortunately, the more I played, the better I felt. I can't complain about a start like this at a Grand Slam, where all opponents are unpredictable."

Djokovic suffered a bleeding right toe during the match, requiring medical attention after the second set. Earlier, he appeared to have a hip issue, repeatedly placing his racket behind his head, a sign of needing more oxygen. At 38, physical condition is a significant concern for Djokovic at each Grand Slam. He withdrew from the Australian Open semi-final earlier this year due to injury and then lost quickly to Jannik Sinner in the subsequent semi-finals in Paris and London, unable to keep pace with his opponent.

Djokovic will have two days of rest, which he described as crucial at Grand Slams, before facing 22-year-old American Zachary Svajda, who had to play through the qualifying rounds. Several other seeded players in Djokovic's half of the draw also advanced after the opening day: Jakub Mensik, Ben Shelton, and Taylor Fritz.

Vy Anh