Defending champion Daniil Medvedev said missing one key opportunity had cost him a spot in the Shanghai Masters' fourth round after he was knocked out in straight sets by 26th-ranked Sebastian Korda on Sunday.
The Russian fell apart in the second set after Korda won the first on a tiebreaker taken to the brink, with the match finishing 7-6 (10/8), 6-2.
"I should have won the tiebreak but didn't," said the world number three afterwards.
"I was, for sure, down mentally after such a first set... In the tiebreak, he actually didn't play that good (compared to the rest of the match). I didn't use this opportunity and I'm going home."
Medvedev fell three games behind an emboldened Korda in the second set, but looked like he might be about to make a comeback with a blistering win in the fourth game.
But the American fought back, taking the next game, and Medvedev grew increasingly agitated, gesticulating in frustration and smashing his racket.
"I feel awesome, I played an incredible match," said 23-year-old Korda at the end, thanking the crowd for their enthusiasm.
"It's been a really long year for me. A lot of injuries, a lot of time off," he said later at a press conference.
"To finally get a really good win like this against a top-5 player is great for me."
'NOT AMAZING'
Medvedev had said the game would be "interesting" for him beforehand, referencing his loss to Korda in their last meeting.
At a press conference after Sunday's match, looking deflated, he summed up his time in China as "not amazing".
He made the final of Beijing's China Open this week but lost to Italian Jannik Sinner.
"Shanghai is really important... I wanted to do better," Medvedev said.
"I felt good being here, so I'm a little bit, not a little bit, I'm very disappointed to lose."
His elimination was watched from the courtside by tournament top seed Carlos Alcaraz.
Medvedev said the 20-year-old Spaniard and Sinner, who also beat Alcaraz in Beijing this week, were the top contenders for his title now.
"But at the same time... Maybe Jannik loses today, Carlos loses tomorrow, and it's all over... That's why tennis is interesting, we can never know," he said with a wry smile.
SINNER WINNER
Medvedev's words seemed almost prophetic in the first set of Sinner's evening match against Argentina's Sebastian Baez.
The world number four had a sluggish start and looked tired, leaning on his racket at one point.
Taking advantage, Baez won the first set by three games.
But at the beginning of the second set, Sinner was transformed, claiming the first three games in quick succession.
The 29th-ranked Baez ultimately couldn't outlast Sinner, with the final score 3-6, 6-3, 6-2.
"I think I handled the situation quite well," the Italian said of being down a set.
"You always have to find a solution when you are down... I just tried to stand a bit more aggressive -- in the first set (Baez) was making a lot of winners and serving very well."
Sinner will next face Ben Shelton, after the American beat Roman Safiullin in three sets 3-6, 6-3, 6-4.
RUUD, RUBLEV VICTORS
Earlier, world number nine Casper Ruud continued his smooth progress through the tournament with another straight-sets win, this time against the United States' Christopher Eubanks.
The Norwegian's next challenge is Fabian Marozsan, who celebrated his birthday by defeating Serbian Dusan Lajovic in straight sets on Sunday.
Poland's Hubert Hurkacz is also through to the fourth round.
World number seven Andrey Rublev is through to the third round after defeating France's Quentin Halys 6-4, 7-5.
Asked about his compatriot Medvedev, Rublev said his playing this year had been "something unreal".
"That he lost here, it sometimes can happen," Rublev said. "To most of the players it's happened more often."
Other top-20 players who exited the tournament on Sunday were Britain's 16th-ranked Cameron Norrie, and Frances Tiafoe, the world number 13.