Carlos Alcaraz’s 15-match unbeaten run in Grand Slam matches ended at the US Open with a sloppy 6-1, 7-5, 6-4 defeat to No. 74 Botic van de Zandschulp in the second round on Thursday evening.

Alcaraz won the French Open in June and Wimbledon in July, bringing his career total to four major championships, including the title at Flushing Meadows in 2022. Ahead of the tournament, he was again the favorite to take home the trophy.

But he never found his groove against van de Zandschulp, a 28-year-old Dutchman. Alcaraz was way off the mark, repeatedly missing the kind of shots he normally makes routinely. After double-faulting and falling two sets to none behind — a deficit he never recovered from — the third-seeded Alcaraz slung his gear bag over his shoulder and trudged to the locker room.

Alcaraz looked toward his coach, 2003 French Open winner Juan Carlos Ferrero, and pointed his right index finger toward his temple. He then waved the finger as if to say, “I’m not thinking clearly.”

He could be forgiven for being confused by what was happening under the closed retractable roof of Arthur Ashe Stadium on a cold evening.

The 21-year-old Spaniard entered the US Open with a 16-2 record, having never been knocked out of the quarterfinals in three previous appearances. It was also Alcaraz’s earliest loss at a major tournament since exiting in the second round of Wimbledon as a teenager in 2021; he has never lost in the first round of a Grand Slam event.

Thursday’s opening set was incredibly lopsided. With van de Zandschulp’s powerful forehands and 132 mph serves finding their mark, Alcaraz never seemed at ease — even though he had won their last two matchups.

Alcaraz failed to produce a winner in that set and nearly doubled his points total, 24-13. The second set was a little better for him, but not enough, and a double fault wrapped up a service break that put van de Zandschulp up 6-5. When Alcaraz pushed a forehand wide to end the next game, van de Zandschulp completed a hold at love that gave him the first two sets after 1 1/2 hours of action.

It didn’t take long for Alcaraz to find himself a break behind in the third set as well, 3-2, but he immediately made a fist — well, with some help, as van de Zandschulp’s double fault resulted in a break that made it 3-all. Alcaraz then held at love and smiled as he headed for the changeover.

However, that smile quickly disappeared as Alcaraz continued to make mistakes and Van de Zandschulp never gave up.