Yafai (right) started quickly to score a standing count in round oneGreat Britain's Galal Yafai will compete for gold after reaching the Olympic final with a relentless display against Kazakhstan's Saken Bibossinov.
The Birmingham fighter, competing in the 52kg flyweight division, was involved in one of the fights of the Tokyo Games and edged a split decision.
A high-paced opening saw Yafai score a standing count with a fine left hand.
And while Bibossinov rallied, the 28-year-old did enough to take the bout on three of the five judges' scorecards.
Bibossinov raised his hands at the bell but was then in tears when the result was read out, the judges scoring the contest 30-27 28-29 29-28 28-29 29-28 in Yafai's favour.
'A ridiculous dream'
Yafai embraced a heartbroken Bibossinov when the result was read outThe success, built around a superb work-rate over nine minutes, sets up a gold-medal match against Carlo Paalam of the Philippines on Saturday and further enhances Britain's success in the ring at the Games.
"I can't believe it. It's ridiculous, it's a dream," Yafai told BBC Sport.
"We're a close-knit team and we support each other. We have six medals now. It shows what GB Boxing is."
Yafai, the younger brother of successful professional fighters Gamal and Kal, stands alongside Lauren Price as Britain's hopes for a first gold medal in the boxing ring at the Games.
Pat McCormack and Ben Whittaker secured silver medals, while Frazer Clarke and Karis Artingstall won bronze.
Earlier on Thursday, Ireland's Kellie Harrington cut an emotional figure after reaching the Olympic final in the women's 60kg division with a 3-2 split decision win over Thailand's Sudaporn Seesondee.
Harrington has become only the second Irish female boxer to win an Olympic medal and will hope to match Katie Taylor's 2012 feat in London by winning gold on Sunday when she takes on Brazil's Beatriz Ferreira, who dominated Finland's Mira Potkonen in the second semi-final.
