NEW YORK – Everyone kept waiting for Carlos Alcaraz to turn things around at the U.S. Open.

Alcaraz figured it would happen at some point. So did his opponent. And surely the Arthur Ashe Stadium crowd and folks tuning in on TV did, too. This is, after all, Carlos Alcaraz we’re talking about — the 21-year-old wunderkind with four Grand Slam titles already, including one at Flushing Meadows as a teen.

A guy at the top of the game right now. A guy expected to accept the mantel from the Big Three of Novak Djokovic, Rafael Nadal, and Roger Federer. A guy who entered the U.S. Open as the favorite and went into the second round in New York on a 15-match winning streak at the majors, with championships at the French Open in June and Wimbledon in July, plus a silver medal at the Paris Olympics in early August.

The best version of Alcaraz never materialized on Thursday night in Arthur Ashe Stadium against 74th-ranked Botic van de Zandschulp, who wound up winning 6-1, 7-5, 6-4, a result as stunning for who won as for how easily he did.

Afterward, the No. 3-ranked Alcaraz sounded like someone a little worried about what it might mean.

“Instead of taking steps forward, I’ve taken steps back mentally. I can’t understand the reason why,” he said during the Spanish portion of his post-match news conference. “I have to check what’s going on with me.”

What Happened to Carlos Alcaraz at the U.S. Open?

It wasn’t just that Alcaraz sounded defeated. It was also that he sounded bewildered.

“I couldn’t see the ball well. … I couldn’t hit it properly. It’s quite a weird sensation,” Alcaraz said. “I’m not well mentally, not strong. I don’t know how to manage the difficult moments, and that’s a problem for me.”

Who is Botic van de Zandschulp?

Across the net was van de Zandschulp, a 28-year-old from the Netherlands who seriously contemplated retirement a few months ago and came to the U.S. Open with a record of 11-18 this season and without back-to-back victories at any tour-level tournament.

He only once has made it as far as the quarterfinals at any Grand Slam tournament, getting to that stage at Flushing Meadows three years ago.