Indonesian qualifier Sony Dwi Kuncoro shocked China's double Olympic champion Lin Dan to reach the final at the Badminton World Federation (BWF) Singapore Open.
The 31-year-old won bronze at the Athens 2004 Olympics but had to qualify for the Super Series event at the Singapore Indoor Stadium.
He had progressed through every round so far in three games and did so again against Lin in the semi-finals, triumphing 21-10, 17-21, 22-20.
It means that a Singapore title continues to elude Lin, the Beijing 2008 and London 2012 men's singles champion.
Kuncoro, a three-time Asian champion and double World Championship medallist, will meet another non-seed in Hong Kong's Ng Ka Long in a surprise final.
The 21-year-old beat South Korea's Son Wan-ho, who deposed of China's number one seed Chen Long in the last eight, 22-20, 21-16.
In the women's competition, Ratchanok Intanon of Thailand remains on course for a third consecutive Super Series crown after reaching the final.
The champion in India and Malaysia knocked out Japan's Akane Yamaguchi 21-12, 22-20 in the semi-finals to set up an intriguing showdown with defending Singapore champion Sun Yu.
The Chinese beat compatriot He Bingjiao 21-10, 21-16 as she bids to defend the title she won a year ago.
Both finals will be played tomorrow alongside the concluding matches in the doubles competitions.
Fu Haifeng and Zhang Nan of China will meet Takeshi Kamura and Keigo Sonoda of Japan in the men's doubles final, with top seeds Misaki Matsutomo and Ayaka Takahashi of Japan playing Indonesia's second seeds Nitya Krishinda Maheswari and Greysia Polii in the women's showpiece.
The mixed final will see South Koreans Ko Sung-hyun and Kim Ha-na meet China's Xu Chen and Ma Jin.