Ratchanok Intanon, the former world champion from Thailand who only just won a fitness race to be ready for this week's All-England Open, made a startling recovery to defeat Olympic champion Carolina Marin on Friday.
Marin had not won a World Super Series event since before her Rio triumph, and although she vowed to rectify that by winning the title this week, she slid from within sight of victory to an improbable 22-20, 13-21, 21-18 defeat.
Marin had been 18-11 up in the final game, having landed a variety of heavy smashes, sliced, round-the-head, and cannonball flat, which looked to be overwhelming the defences of her young rival.
But the Thai then started to take the attacking initiative away from the aggressive Spaniard, landing three good blows herself and suddenly generating some momentum.
Surprisingly Marin was unable to wrest it back, and at 18-16 was spoken to by the umpire, apparently for something she said.
By that stage she had begun taking risks to get the elusive last three points, but this resulted in a mid-court jab into the net and a kill into the net, followed by a stunning defeat when she cleared the shuttle long.
"I was in control of the match at 18-11 but I lost focus," Marin reckoned.
"My opponent rushed me and I can't understand why I lost it."
Ratchanok next plays a surprise semi-finalist, Akane Yamaguchi of Japan, whose 21-23, 21-14, 22-20 victory over the fourth-seeded Sun Yu ended the Chinese bid to regain a women's singles title they have dominated for a large part of two decades.
Earlier Tai Tzu Ying, the top-seeded World Super Series winner from Taiwan, reached the semi-final with an impressive 21-14, 21-10 win over Pusarla Sindhu, the Olympic siler medallist from India.
After trailing 5-9 in the first game, Tai found ways of taming the Sindhu smash which was timed at 223 mph at last year's All-England.
"I tried to find loopholes in her attack," Tai explained.
Sindhu's Olympic final with Marin set TV viewing records, and was watched by 17 million viewers in India, and utterly changed her life, bringing the rewards of cars, land and a government job and a million and a half pounds worth of cash.
Now however the chance of glory at the world's oldest tournament slipped rapidly away.
It meant that both leading Indian players had gone out. Earlier Saina Nehwal was narrowly beaten 22-20, 22-20 by Sung Ji-hyun of Korea after leading 17-12 in the first game. Sung now plays Tai.