Novak Djokovic went down in straight sets to Hubert Hurkacz on Friday, exiting the Shanghai Masters in his first match after memorably winning the China Open this week.
Big-serving Hurkacz, the 2023 champion in Shanghai, won 6-4, 6-3 as the 39-year-old former world No 1 faltered against an opponent a decade his junior.
"I didn't feel myself on the court," the Serbian veteran said afterwards.
"It's a super-quick surface, completely different from Beijing. If you lose your serve, it's enough to lose a match."
Djokovic was playing three days after winning the title in Beijing, where he has still never lost a match on the professional Tour.
He hunched over and squatted down between points on a cool evening in Shanghai while a lively Hurkacz refused to give much away.
Djokovic was broken in the fourth game of the second set as he double-faulted to give Hurkacz a 3-1 lead.
The Pole held his serve to see out the win and will face either Italy's Lorenzo Musetti or Chinese wildcard Zhou Yi in the third round.
"It's very difficult to return his serve, almost impossible," Djokovic said of his opponent, who sent down 13 aces across the one-hour-and-28-minute match.
"I didn't adjust, and it was a really tough draw for me to play him in the first match-up."
Hurkacz had advanced to the Beijing semifinals but ended his match early due to a strained muscle.
It was his first-ever victory against Djokovic in nine meetings on the Tour.
"It was a challenging match, always," Hurkacz said.
"I was pleased with how I performed, how I received in important moments."
ZVEREV SURVIVES SCARE
Earlier, top seed Alexander Zverev churned out a win over Chinese wildcard Wu Yibing 6-4, 7-6 (7/4), and will next play Quentin Halys of France.
A dive left the German world No 2 grimacing and grabbing his left ankle during the 11th game of the second set, with Wu, ranked 113th, going 6-5 up.
But the 29-year-old held serve and forced a tie-break, capitalising on a series of errors to win on his second match point when the home hope fired long.
"Credit to him, he was playing amazing tennis," Zverev told the crowd afterwards.
"He hits every ball as hard as he can."
Zverev is on track to end the year at No 1 after Jannik Sinner announced he was ending his season due to injury.
BIRTHDAY JOY FOR SHELTON
A gritty Ben Shelton beat Germany's Daniel Altmaier 6-3, 7-6 (8/6) and will play France's Arthur Gea in the third round.
It was a fitting present for the American third seed, who turned 24 on Friday, though he hinted he may go easy on the celebrations, telling an on-court interviewer: "I hate cake."
Frenchman Adrian Mannarino upset sixth-seeded Flavio Cobolli 6-1, 4-6, 6-3 to set up a tie against Karen Khachanov.
And Japanese qualifier Rei Sakamoto beat Russia's Andrey Rublev 6-4, 6-4 to earn a match against ninth-seeded Alex de Minaur.