Luke Campbell and John Joe Nevin scrapped through 21/2 remarkably even rounds, their British and Irish fans getting more uneasy with every blow.
And then Nevin walked into a big right hand from his British opponent.
Nevin ended up on his back.
Campbell ended up with a gold medal, largely on the strength of that one spectacular punch.
The British bantamweight fought back tears in the ring after the final verdict made him an Olympic champion. Campbell beat his rival 14-11 Saturday night, securing Britain's first gold in his weight division since 1908.
"I won. Can't believe it," Campbell said. "That's what was going through my mind. It's a day I've dreamed of for a long, long time."
Campbell's solemn, teary rendition of "God Save the Queen" in front of his adoring fans had little in common with the other four gold-medal celebrations at ExCel arena.
Ukrainian heavyweight Oleksandr Usyk put on a show that overshadowed even his 14-11 victory over Italy's Clemente Russo. The intimidating 6-foot-3 bruiser with the distinctive haircut broke into an astonishingly nimble Cossack dance in the center of the ring, bouncing and leaping with carefree abandon.
And when light flyweight Zou Shiming of China defended his Beijing gold medal with a 13-10 win over Kaeo Pongprayoon, his Thai opponent collapsed on the canvas in fury and pain, eventually leaving the ring in tears.
"I feel that I won, and I could see that the crowd thought I won," Pongprayoon said. "I don't know why I lost. I think the points system at the Olympics is wrong or strange."
Just another typical day at an Olympic boxing tournament -- and there are still five more gold-medal bouts on Sunday.
Light welterweight Roniel Iglesias beat Ukraine's Denys Berinchyk 22-15 for Cuba's first boxing gold in London after failing to win any in Beijing. Middleweight Ryota Murata then narrowly won the second boxing gold medal in Japan's Olympic history, beating Brazil's Esquiva Falcao 14-13 on the strength of a two-point holding penalty against Falcao in the final round.
But most of the crowd came to cheer Campbell, the 24-year-old father who locked up Britain's second gold medal at its home Olympics following Nicola Adams' flyweight victory in the women's tournament. Campbell also won the rubber match in his friendly rivalry with Nevin, who beat him soundly in the 2009 world championships before losing to Campbell on a tiebreaker last year.
Their Olympic bout was still in doubt when Campbell connected with a punch that will loom large in Britain's boxing history. Campbell had few thoughts as he waited for the eight-count on Nevin.
"After that, I just had to carry on what I was doing and not be silly," Campbell said.
Nevin, a two-time Olympian, was stone-faced after the decision, but embraced his rival.
"I would have given my right arm (even) for a bronze medal before the games, so this is a dream come true for me," Nevin said. "My mother has decided the medal is going to go in her cupboard."
Ireland is leaving London with four boxing medals, including Katie Taylor's gold.
Usyk put a sharp finish on a division filled with ugly fights in London by overpowering Russo, who equaled the silver medal he took home from Beijing. Russo's hold-filled strategy couldn't contain Usyk, whose hair is in a traditional chub haircut -- a shaved head with a long, flowing lock coming straight off the top.
Usyk appeared to knock down Russo with a big left hand early in the 2nd round, but Russo wasn't given an eight-count. Usyk still controlled the bout despite an improved effort from Russo, who embraced him shortly before Usyk broke into his impressive dance moves.
Usyk is Ukraine's third boxing gold medalist, joining Wladimir Klitschko and Vasyl Lomachenko, who fights Sunday for his second gold. The Ukrainian team will lead the Olympic field with five boxing medals.
But Iglesias stood up to one of the toughest fighters in the London field, picking apart the hard-nosed Berinchyk with a masterful boxing display and denying the other Ukrainian fighter with that distinctive haircut.
Iglesias was a silver medalist in 2008, but returned with a stellar run through the 2012 tournament. Cuba's 33 boxing gold medals are second in Olympic history to the U.S. team's 48.
Murata joined Zou in getting an enormous benefit from a final-round penalty when he held off Falcao, who didn't appear bothered by the verdict. Murata, a veteran amateur who produced the best results of his career in London with a methodical style of fighting, is the only Japanese man to win gold in boxing since Takao Sakurai won at bantamweight at the 1964 Tokyo Olympics.
Falcao and his brother, Yamaguchi, both fell just short of winning Brazil's first Olympic boxing gold, with Yamaguchi winning a bronze medal as a light heavyweight. Brazil had won just one boxing medal in its entire Olympic history before the Falcao brothers came through in London -- an auspicious start to the four-year process of preparing for the Brazilians' own home Olympics in Rio.