NEW YORK — For the second contest in a row at this US Open, Novak Djokovic appeared a bit sluggish, a bit off, for a stretch. This time, he even dropped the opening set. And then, as always at Flushing Meadows, the 24-time Grand Slam champion progressed to the third round.

Djokovic improved to 36-0 across the first and second rounds in New York, a place he’s won four championships, by coming back to beat 145th-ranked American qualifier Zachary Svajda 6-7 (5), 6-3, 6-3, 6-1 on Wednesday.

“I really tried to soak it in and enjoy the moment, especially when I won the first set,” said Svajda, a 22-year-old from San Diego. “It kind of shocked me. I was like, ‘Wow!'”

Playing the opening match of the day session at Arthur Ashe Stadium for the first time since 2014, Djokovic improved to 54-45 in majors after losing the opening set — the most such wins by any man in the Open era (since 1968).

Asked on court afterward how he felt in his first competition since losing to eventual champion Jannik Sinner in the Wimbledon semifinals on July 11 while hindered by a groin injury, Djokovic replied: “Not that great, to be honest.”

Svajda noticed.

“He was missing a little bit,” said Svajda, who got cramps in his legs and arms as the match wore on. “He was getting a little frustrated.”

At his news conference later, the 38-year-old Djokovic spoke a little more about his mood.

“It’s not a motivation thing. It’s just like me a bit frustrated with my game, and then I kind of go through stuff internally that — you don’t want to know the details what I’m going through and telling myself,” he explained after getting to the third round at a major for the 75th time, breaking a tie with Roger Federer for the most such appearances by a man.

“I’m just trying to be locked in. Just trying to solve the riddle once I’m on the court,” Djokovic continued. “It’s not like I’m not finding joy on the court competing. I enjoy competing, but I don’t enjoy not playing well. That’s why I put extra pressure on myself and my team to be better the next day, the next match.”

That will come against Cam Norrie, a British left-hander who reached the semifinals at Wimbledon in 2022, or Francisco Comesana of Argentina.

Whichever man it is will face the task that Svajda did Wednesday against Djokovic.

“He does everything so well, which is incredible,” Svajda said. “I was talking to my team and coaches before, trying to figure it out. It’s Novak Djokovic, so there’s not a big weakness.”

In other men’s singles second-round results, No. 20 Jiri Lehecka defeated Tomas Martin Etcheverry 3-6, 6-0, 6-2, 6-4. And Czechia’s Tomas Machac, the No. 21 seed, got past Brazilian 19-year-old sensation Joao Fonseca 7-6 (4), 6-2, 6-3.

No. 12 Casper Ruud, whose 0-3 record in Grand Slam finals includes a loss to Carlos Alcaraz at Flushing Meadows in 2022, was eliminated 6-4, 3-6, 3-6, 6-4, 7-5 by Raphael Collignon of Belgium.

The 107th-ranked Collignon had never won a match at a major or played a five-setter until this tournament.

Another seeded to player to go down was No. 18 Alejandro Davidovich Fokina, beaten by Arthur Rinderknech 6-4, 3-6, 2-6, 6-2, 6-3.

ESPN Research and The Associated Press contributed to this report.