Number two seed Momota, whose career has been in free fall since a car crash more than two years ago left him badly hurt, limped out after another meek performance in front of a stunned crowd in Tokyo.

Momota, once badminton's undisputed king, looked a shadow of the player that won a record 11 titles in 2019, and he pulled no punches when analyzing his own performance after the match.

"I was so scared of making mistakes that I shrunk within myself a little, and I think that was why I lost," the crestfallen 27-year-old told reporters.

"I realized that midway through the match, but I couldn't do anything to fix it. I was weak-spirited and that's so frustrating."

Momota dumped shot after shot into the net and was powerless to stop world number 18 Prannoy from taking control early in the match.

Momota vowed to try to get back to his former position at badminton's summit but he said he would need some time to get over this latest disappointment.

"I think I used to win titles too easily," he said.

"It became a matter of course that I would win them, but it's difficult and some players never win even one."

"I don't think at all that I'm not capable of winning titles," he added.

Prannoy will play in the next round against his Indian compatriot Lakshya Sen, who advanced with a 21-17, 21-10 win over Spain's Luis Enrique Penalver.

"I can't really be happy about what I've done because you don't have time for that," Prannoy said.

"You have to get ready for what's to come next tomorrow and hopefully keep getting better."

Malaysian number five seed Lee Zii Jia also booked his place in the next round with a comfortable 21-9, 21-12 win over Portugal's Bernardo Atilano.

Lee is aiming to become the first Malaysian ever to win a world badminton title and he said he was "feeling good" after making short work of Atilano.

"I think the real challenge will be tomorrow, and my opponent will be tougher than today," said the 24-year-old.

"It's a big challenge for me — I want to be the first to win the world championships from Malaysia. I think everyone has a big chance to win so we will see."

Defending champion Loh Kean Yew of Singapore had to fend off a furious second-game fightback from Guatemala's Kevin Cordon before closing out their contest 21-12, 11-21, 21-12.

Number eight seed Loh played down the pressure of arriving in Tokyo as the reigning champion and said he intended to "treat it like any other tournament".

"I'm definitely happy on the winning side, always," he said.

India's Commonwealth Games bronze medalist Kidambi Srikanth was stunned 21-9, 21-17 by China's unseeded Zhao Junpeng.

Number 12 seed Srikanth, the silver medalist at last year's world championships and part of India's Thomas Cup-winning team in May, said he "could have maybe played better".

"He just played well when it really mattered," said the former world number one.