Sixth seed Lee Zii Jia of Malaysia stunned top-ranked Kento Momota of Japan 21-16, 21-19 in the All England Open quarter-finals in Birmingham yesterday.
The 26-year-old Japanese was playing in his first tournament on the international stage in 14 months after suffering facial injuries in a traffic accident in Malaysia and then testing Covid-19 positive.
Momota made a successful return to domestic badminton by winning the All-Japan Championship in December.
He was scheduled to play in three tournaments in Bangkok in January but tested positive just before he travelled to Thailand.
The Malaysian lost in all six previous meetings against the two-time world champion.
"I've never beaten him before, so this is a very special moment for me," Lee said.
"I did a lot of studying about Momota. Every time I played him, it seems like there's a big gap between us. I always discuss about what strategy I have to play against him, we worked a lot on that. Today is a big win for us."
It will be his second semi-final appearance in the All England for Lee, having reached the same stage last year before bowing out to eventual champion Viktor Axelsen of Denmark.
In today's semi-finals, the 22-year-old Malaysian will meet the Netherlands' Mark Caljouw, who beat India's Lakshya Sen 21-17, 16-21, 21-17.
In the men's doubles, Japan's Takeshi Kamura and Keigo Sonoda beat England's Marcus Ellis and Chris Langridge 21-19, 9-21, 21-8.
In the women's doubles, top-seeded Yuki Fukushima and Sayaka Hirota defeated home players Chloe Birch and Lauren Smith, who were seeded seventh, 14-21, 21-12, 21-14 to advance to the semi-finals.
The Netherlands' Selena Piek and Cheryl Seinen also reached the last four after beating India's Ashwini Ponnappa and Reddy N Sikki 24-22, 21-12.
The tournament ends tomorrow.