The Dutch veteran denied 21-year-old Gea a slice of Grand Slam history. The French player had been vying to become the first men's lucky loser to reach a Grand Slam quarter-final.
A dozen lucky losers - players who lost in qualifying but made it into the draw when someone withdrew - had made it to the round of 16 at this level, but none had gone further.
Gea, ranked 87th in the world, lost in the final round of qualifying but reached the main draw when 18th-seeded Casper Ruud withdrew with a back injury.
He nearly broke through, but the Netherlands' van de Zandschulp saved a match point in the third set and almost two hours later sealed a win that put him into the quarter-finals for the first time since 2021.

The five-hour, 13-minute marathon was just shy of the record-longest US Open match, Dan Evans's five-hour, 35-minute first-round victory over Karen Khachanov in 2024.
An exhausted van de Zandschulp told the crowd he didn't know how he did it.
"No clue actually," the 30-year-old said. "Crazy comeback - five hours, 15 minutes, still standing, so that's a good thing.
"I think this is probably even better than the first quarter-final I made here," added van de Zandschulp. “It's been some tough years, but started to play better this year again.
"It hasn't really sunk in yet, but I think tomorrow it's going to be a great feeling."
Next up for van de Zandschulp will be top-seeded Alexander Zverev.
The Dutch player has some history with upsets at the US Open. In 2024, he stunned then third-seeded Carlos Alcaraz in straight sets in the second round.
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