Yang Liu of China stunned welterweight defending champion Chen Nien-chin of Chinese Taipei here at the International Boxing Association (AIBA) Women's World Championships.
The two boxers met in the quarter-finals, with Yang edging past the welterweight top seed 3-2.
Now guaranteed at least a bronze medal, her semi-final opponent will be Lovlina Borgohain of India, a 4-1 winner against Karolina Koszewska of Poland.
Saadat Dalgatova also recorded a 4-1 victory, delighting the home support as she overcame Pan American Games champion Oshae Jones of the United States.
Busenaz Sürmeneli unanimously defeated Christina Desmond of Ireland to set up a clash with Dalgatova.
There was another upset in the light flyweight division, Manju Rani of India triumphing 4-1 against top seed Kim Hyang-mi of North Korea.
Chuthamat Raksat of Thailand will fight Rani next, having secured a unanimous win over Sevda Asenova of Bulgaria.
England's Demie Resztan then narrowly defeated Roberta Bonatti of Italy 3-2 and is scheduled to come up against home favourite Ekaterina Paltceva.
The Russian boxer dominated against Rabab Cheddar to receive a unanimous decision.
Mira Potkonen continued her impressive campaign in the lightweight division, with the top seed beating Amy Broadhurst of Ireland 5-0.
Wang Cong of China got the same result against Monkhor Namuun of Mongolia to set up a semi-final bout with Potkonen.
Superrr Upset! 🚨— Boxing Federation (@BFI_official) October 10, 2019
Sensational comeback by Manju!🔥
Despite the stiff challenge, Manju Rani remained calm under pressure and secured a 4️⃣-1️⃣ win over the top seed- Kim Hyang Mi of 🇰🇵 at the#AIBAWomenWorldBoxingChampionship !
Kudos on the huge win!👏#PunchMeinHaiDum #boxing pic.twitter.com/xjYNbL1HfB
Pan American champion Beatriz Ferreira survived a scare against Russia's Natalia Shadrina, with the Brazilian triumphing 3-2.
Her next opponent will be Rashida Ellis of the US, a 4-1 victor against Sudaporn Seesondee.
Huang Hsiao-wen of Chinese Taipei continued her bantamweight title defence with a unanimous win over Aira Villegas of the Philippines.
She will battle against Jamuna Boro next, with the Indian boxer overcoming Ursula Gottlob of Germany 4-1.
Caroline Cruveillier of France unanimously defeated Antonia Konstantopoulou of Australia, with Mikiah Kreps of the US waiting in the semi-finals.
Kreps had beaten Dina Zholaman of Kazakhstan 4-1.
In the light heavyweight division, defending champion Wang Lina of China recorded a unanimous victory against Fariza Sholtay of Kazakhstan.
She will have to face a home favourite next, coming up against Zenfira Magomedalieva of Russia, a 5-0 winner over Ezozakhon Melieva of Uzbekistan.
Nguyễn Thị Hurong of Vietnam and Elif Güneri of Turkey make up the remaining final after they both squeezed past their respective opponents, Krystal Graham of the US and Irina Schönberger of Germany, 3-2.
The semi-finals are on Friday (September 12) following a rest day tomorrow.