Botic van de Zandschulp was paying as much as 50-1 to defeat Carlos Alcaraz in the US Open second round.
The 28-year-old Dutchman wasn't given a chance by anyone to defeat the three-time grand slam major winner.
Instead, he thrashed Alcaraz in straight sets 6-1 7-5 6-4 in two hours, 21 minutes to reach the third round at Flushing Meadows.
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In one of the greatest upsets in US Open history, Van de Zandschulp got the jump to blitz the third seed in the first set before weathering several comebacks in the second and third.
Why Carlos Alcaraz lost to Botic van de Zandschulp at US Open
Alcaraz didn't look to be struggling with injury and was just beaten fair-and-square by the 74th-ranked Dutchman, who has been ranked as high as 22 and reached the last eight at US Open 2021.
But it appeared that fatigue may have caught up with Alcaraz, who won the last two grand slam titles at the French Open and Wimbledon, before winning a silver medal at the Paris Olympics.
Tennis legend John McEnroe felt that after the level of Alcaraz's performance, it might have been better for the young gun to have rested after the heavy 2024 schedule.
“In hindsight, he probably would have been better off not playing at all,” he told Eurosport.
“Given everything that’s happened, emotionally, it’s going to be a big ask for him to win this tournament.”
How does Alcaraz's defeat affect the men's US Open draw?
Alcaraz's loss makes the path easier for world no.1 Jannik Sinner to reach the US Open final, with the two initially destined to meet in the semi-finals.
In Alcaraz's quarter of the draw, 10th seed Alex de Minaur looks set to benefit the most as the highest-ranked player in the section.
Other players who will contend to win the quarter missing Alcaraz include 25th seed Josh Draper and 30th seed Matteo Arnaldi.
Alcaraz is the highest-seeded player eliminated from the US Open so far, with seventh seed Hubert Hurkacz and 11th seed Stefanos Tsitsipas also already out.