Unseeded Japanese badminton duo Miyuki Maeda and Satoko Suetsuna enjoyed the "win of their lives" when they rallied from the brink to eliminate Olympic champions Yang Wei and Zhang Jiewen in the women's doubles on Monday.
The top seeded Chinese were 2 points from winning the match at 19-16 in the second game, but committed a series of errors and lost it 23-21.
The rattled Yang and Zhang crumbled in the second half of game three, giving up 12 of the final 17 points to go down 14-21.
"This was the biggest win of our lives," Suetsuna said. "They are the Olympic champions so even when we had 20 points in the third game we couldn't take anything for granted. It wasn't until we got that final point that we could celebrate."
The result advances the Japanese pair to the semi-finals and dents China's hopes for gold in the event, although the second and third seeds in women's doubles are also Chinese.
Denmark's singles medal dreams also suffered on Monday when women's sixth seed Tine Rasmussen lost in three hard-fought games to unseeded Maria Kristin Yulianti of Indonesia, and in the men's event Kenneth Jonassen lost to South Korea's Lee Hyunil, who was not seeded but was recognised as a major threat.
"He was the only player nobody wanted to meet," said Jonassen, who was appearing in his third Olympics.
Denmark's Peter Hoeeg Gade, who made the quarterfinals in Athens, plays later on Monday.