Japanese world badminton number one Kento Momota blamed his own "weakness" as he crashed out of the Tokyo Olympics in the first round on Wednesday.
Unseeded South Korean Heo Kwang-hee beat Momota 21-15, 21-19 to end his gold-medal bid after just two games, a day after Japanese tennis superstar Naomi Osaka also made an early exit.
Momota won a record 11 titles in 2019 to cement his place as the undisputed best badminton player in the world.
But he was almost forced to retire last year after a car crash that left him with career-threatening injuries, and he admitted his killer instinct of old had not yet returned.
"Previously, when a game went like this, I would be able to recover and think clearly," said a visibly stunned Momota.
"I would have been able to pull through. But I couldn't recover tonight, and that's down to my weakness."
Momota fractured his eye socket in the accident in January last year which killed the driver of the vehicle taking him to the airport after winning the Malaysia Masters.
He suffered double vision and needed surgery on a bone near his eye that delayed his comeback, leaving him fearing his career was over.
He returned to make his Olympic debut in Tokyo -- five years after being banned from the 2016 Rio Games for illegal gambling.
But his confidence deserted him when Heo began to gain a foothold in the first game, and he was unable to reassert control.
"I was 10-5 up in the first game, I wasn't moving badly and I had an attacking image in my mind," said Momota.
"But then I lost a few points in a row and my opponent beat me to 11, which affected me mentally and I didn't recover. I came up short."
Momota admitted making his Olympic debut had overwhelmed him.
"It's really difficult to go about things the way you usually do when you're playing on this stage," he said.
"A lot of things happened, but thanks to the efforts of many people I got to feel the tension and experience what it's like to play at an Olympics. I really appreciate that."
Momota smiled incredulously as his shots failed to find their range early in the game, but looked ashen-faced when it became clear that he was in serious danger.
He then sealed his own fate when he hit the net to end the match.
"I think I wanted to win too much," he said. "Rather than him being able to read me, I didn't have any margin for error and I started to play within myself."
Momota's early exit follows similar upsets for high-profile Japanese athletes, including tennis player Osaka and gymnast Kohei Uchimura.
Badminton number two seed Chou Tien-Chen also suffered a fright on Wednesday, but saw off 19-year-old Canadian Brian Yang 21-18, 16-21, 22-20.