Luke Campbell became the first British boxer to guarantee a medal by posting a narrow victory on Sunday.
Bantamweight Campbell edged out old rival Detelin Dalakliev 16-15 in his quarter-final.
The Hull fighter will now fight Japan's Satoshi Shimizu on Friday with a place in the Olympic final at stake. Even if he loses, he is guaranteed a bronze medal.
Campbell beat the Bulgarian to win the 2008 European title and also in last year's World Championships.
After his latest triumph, he said: "When I've beaten him in the past that's been and gone but tonight comes round just once every four years. I'm overwhelmed at the moment and I'm proud of myself that I'm going to bring a medal home to my little boy.
"All the sacrifices and discipline I've had to put in is all worthwhile, but this is just the start. I'm here for gold. I train to win and I fight to win, and I'm going in to win my next fight and then to win my gold medal.''
Dalakliev, the 2009 world champion, shaded the first round 4-3 on the judges' cards.
The second was split 5-5 before Campbell was given the verdict courtesy of an exciting 8-6 final round.
