The world number 74 outclassed third seed Alcaraz 6-1, 7-5, 6-4 under the lights at Arthur Ashe Stadium on Thursday to move past the second round of a Grand Slam for the first time since mid-2022.
It was the biggest win of his career and came against an opponent who had won back-to-back Grand Slams and was on a 15-match winning streak at the majors.
"Maybe I'm still processing it," Van de Zandschulp said shortly after his stunning win over the 2022 champion.
"Maybe in a couple of hours or tomorrow I feel a little bit more emotional with what happened tonight."
Van de Zandschulp bruised a bone in his left foot last year and later tore ankle ligaments, before dealing with an infection on his right foot. He began questioning his future in the sport after a first-round defeat at the French Open in May.
"At the time I said it, I was thinking about it. It was just more the way things were going," said Van de Zandschulp, who was ranked 115th in April.
"I got injured last year. Still had some troubles with the injury from last year. That was for me like, if I have to keep playing with the pain I had, then there was a chance maybe I would stop playing.
"Of course, I would give myself to the end of the year and see how everything was progressing. Yeah, of course, there was a serious thought."
The Dutchman, who steadily built up his game playing Challenger tournaments, faces Briton Jack Draper in the third round and expects matches to get even tougher as he bids to better his quarter-final run in New York three years ago.
"Draper is a really good player, having a good season this year. Big serve and big strokes. So it's going to be, again, a really tough match," Van de Zandschulp said.
"I'm looking forward to the rest of the tournament. I think everybody who is still left in the draw are amazing players. So, yeah, every match is going to be tough."
