Watch: Botic van de Zandschulp stays stoic after huge U.S. Open upset over Carlos Alcaraz

Before the match, he jokingly said he hoped that Alcaraz wouldn't be at 100% and that he could use "a little help" to get through the Spanish ace. 

While Alcaraz didn't show any signs of injury, he didn't look himself, especially with his groundstrokes and return game. The 21-year-old won only 33/95 of his receiving points and committed an uncharacteristic 27 unforced errors, giving van de Zandschulp plenty of opportunities to capitalize on his off night.

Biggest upset ever?

After his monumental win, van de Zandschulp revealed he was on the verge of retirement in 2023 due to his inability to qualify for any of the majors. He had to play challenger events to keep his career afloat. 

Considering that a player at such a stage of his career defeated Alcaraz — a stud in his athletic prime — led some to label Thursday's outcome as arguably the biggest upset of all time.

As for Alcaraz, it was one of those nights when he couldn't find his rhythm. In his post-match news conference, a subdued Alcaraz admitted to feelings of "confusion" and being overcome by "emotions I couldn't control." The Spaniard also said van de Zandschulp didn't give him "any free points" and made him work for every point.

"I didn't know how to manage that," Alcaraz said of not getting any freebies. "I have to think about it. I have to learn from it."

One couldn't help but compare the loss to Rafael Nadal's first-round defeat to Steve Darcis at the 2013 Wimbledon. Nadal bounced back by winning the U.S. Open that year. Could Alcaraz do the same at the 2025 Australian Open? 

Thursday's outcome was ultimately a reminder that even the greats have off nights.