BANGKOK: Badminton world number one Akane Yamaguchi suffered a stunning Thomas and Uber Cup defeat on Wednesday at the hands of a teenage rookie ranked more than 300 places below her.
Indonesia's Bilqis Prasista, 18, saw off Japan's world champion 21-19, 21-19 in 35 minutes at Bangkok's Impact Arena.
But Japan roared back to beat the Indonesians 4-1 and top Group A. Both teams have qualified for the quarter-finals of the women's Uber Cup.
"It's unbelievable. I could never imagine beating Akane Yamaguchi," Prasista, 333rd in the world rankings, said.
"I just wanted to make her run and chase the shuttle so it was no fun for her. That was the key."
The teenager made her mark early, leaving Yamaguchi scoreless as she jumped into a four-point lead in the first game.
Yamaguchi briefly recovered but came unstuck in the face of lethal net shots and smashes from her gutsy opponent.
Yamaguchi grabbed an early six-point lead in the second game before Prasista levelled the scores with a run of points, then inched to match point and a surprise victory.
It was a hat-trick of wins for Prasista, who beat German Florentine Schoeffski and France's Yaelle Hoyaux in recent days.
A disappointed Yamaguchi said the drift in the arena had made it difficult to control the shuttlecock.
"I couldn't control the game," the 24-year-old told reporters.
Elsewhere, South Korea thrashed India 5-0 to top Group D with An Se-young too good for P.V. Sindhu.
The world number four claimed victory in 42 minutes, 21-15, 21-14, over the seventh-ranked Sindhu.
The Koreans and India are also both into the last eight of the competition.