British lightwelterweight Tom Stalker bowed out following Wednesday's quarter-final defeat, while Ireland's Paddy Barnes wants just a point against reigning Olympic light flyweight champion Zou Shiming.
Stalker, the British team captain, was left devastated by his 23-22 quarter-final defeat to Mongolia's Munkh-Erdene Uranchimeg.
"He's inconsolable to be honest," admitted British coach Dave Alloway, with four British boxers already in the semi-finals and flyweight Nicola Adams to contest Thursday's women's flyweight final against China's Ren Cancan.
"He was one bout away from a medal and to lose by a point is hard on him."
Stalker's devastation was in sharp contrast to Uranchimeg's delight.
"My soul is full of emotion," said the 30-year-old Mongolian.
"I have been in the Olympics three times now - Athens, Beijing and now London. It has been my long-standing dream to get a medal, which I have now achieved."
Stalker's exit means Uranchimeg faces Ukraine's Denys Berinchyk, the world silver medallist, in the semi-finals after his convincing 21-13 win over Australia's Jeffrey Horn.
With Brazil's world champion Everton Lopes already out, Cuba's Roniel Iglesias will take on Italy's Vincenzo Mangiacapre in the other semi-final after they both came through their last eight bouts.
In Friday's flyweight semi-finals, Barnes has said his only goal is to a take a point of China's world champion Zou.
The Irishman still remembers the humiliation of losing 15-0 to the 31-year-old world and Olympic champion in the semi-finals of Beijing 2008.
Having guaranteed himself at least a bronze after his 23-18 quarter-final win over India's Devendro Laishram, the 25-year-old says low expectations.
"Bronze medals are for losers. I am fighting a guy in the next fight who beat me 15-0 in Beijing, so my plan in the next fight is to just score a point," said Belfast-born Barnes who brought home a bronze from Beijing.
"If I can just get that one point, I can go home a happy man."
China's boxing icon Zou, the Asian champion, put in a solid display in his 13-10 victory over Kazakhstan's Birzhan Zhakypov having hammered Cuba's Yosbany Veita 26-4 in the Round of 16.
In the other semi-final, 32-year-old Kaeo Pongprayoon of Thailand faces Russia's David Ayrapetyan in Friday's semi-final and is keeping it mum about his chances of gold.
"I want to say to my mum 'I have done it mum. I am going to bring back a medal'," he said after his 16-10 quarter-final win over Bulgaria's Aleksandar Aleksandrov."
"This is my first Olympics and I am not going home empty-handed."
There was a shock in the first light welterweight quarter-final as Cuba's world champion Julio la Cruz was beaten 18-15 by Brazil's Yamaguchi Falcao, who faces Russia's Egor Mekhontcev in Friday's semi-final.
Ukraine's Oleksandr Gvozdyk upset Algeria's Abdelhafid Benchabla for a 19-17 quarter-final win to meet Kazakhstan's Adilbek Niyazymbetov in Friday's other semi.
A disgruntled Algerian threw what appeared to be a desklamp from the stands into the area surrounding the ring in disgust after Benchabla's defeat.