Rafael Nadal suffered his first loss of the year in his 21st match, losing in straight sets to Taylor Fritz in the Indian Wells final.
Nadal, 35, looked out of place and quickly lost 4-0 before leaving the court for treatment.
He looked more comfortable on his return but struggled to break the determined Fritz, who won 6-3 7-6 (7-5).
“It’s one of those childhood dreams that you don’t even think will come true,” Fritz, 24, said.
He saved two break points at 5-5 in the second set before winning the tiebreak to secure his first Masters 1000 win.
Fritz’s win meant he became the first American to win at Indian Wells since Andre Agassi in 2001.
There were concerns about his fitness after he suffered an ankle injury in the semi-final win over Andrey Rublev, but he did not show any ill effects during the win.
“I can’t even begin to describe how ridiculous it is to play the way I could play today, I’ve never been in as much pain as before a match,” Fritz said.
“I took a couple of steps and screamed. I tried to be tough and we did a great job before the match.
“I went through a rollercoaster of emotions and suddenly became really happy, thinking that maybe I can play, but it didn’t affect me at all.”
Spaniard Nadal, who won the Australian Open earlier this year, won his previous 20 matches in 2022.
But he made 34 unforced errors in the match against Fritz’s 22.
“I tried my best for the last two weeks, today it was impossible. I think I fought well until the end,” Nadal said.
“It has been a long time since I had the opportunity to play here, but I am very happy to be back and really enjoy every day that I spend here.
“We can be very pleased with how things have gone over the last couple of months.”