Britain's Matthew Pinsent claimed an historic fourth Olympic gold medal when his crew pipped world champions Canada in the men's coxless four on Saturday.
Pinsent and Sydney champion James Cracknell, Ed Coode and Steve Williams won by the narrowest of margins in a time of six minutes 6.98 seconds.
The Canadian crew put the Britons under heavy pressure in the final stages.
But the GB four dug deep to edge them out in a photo finish by 0.08 seconds, while Italy took bronze.
Pinsent, 33, won his first gold with Steve Redgrave in 1992 and has never lost an Olympic race, also triumphing at Atlanta 1996 and Sydney 2000.
The victory, cheered on by a swell of Union Jack-clad supporters from the stands, was a dream ending for the British crew after a difficult season marred by injury.
The quartet took an early lead in the race, moving just 0.44 seconds ahead of the Canadian danger boat at the 500m mark with Australia third.
But Canada clawed their way in front by the third quarter to set up a tense finale.
Pinsent's crew replied by delving deep into their reserves and as they raced to the line it was impossible to tell which boat held the advantage.
Following the photo finish, there was an anxious wait before the scoreboard flashed up confirmation of Britain's dramatic win.
The difference between first and second... 0.08 seconds
"It is really hard to get any perspective on it at the moment," an emotional Pinsent said afterwards.
"I thought we rowed a really good race and controlled it nicely in the middle.
"We knew if we got to halfway and we were with them they were going to be in more trouble than us. Then we just moved on."
Cracknell, who rowed with Pinsent and Redgrave in Britain's coxless four triumph at the last Olympics, said the win was even sweeter after the ups and downs the boat endured this season.
"Four years of emotion went into those six minutes," said Cracknell.
"There has been a lot of crying and shouting in the last 48 hours and it is incredibly hard.
"After such a tough season, it is very mentally gratifying to produce it in an Olympic final, and to do it like that, by a few hundredths of a second."
German coach Jurgen Grobler was overwhelmed by the victory, saying: "This is the most emotional situation I have ever had.
"This was maybe the toughest season we had so far. We had problems throughout the season and it is a big relief for me and British rowing.
"We had to rely on preparation and we made really good progress and the crew was really together."
Coode was also delighted to claim his first gold medal after coming in at short notice to replace Alex Partridge, who withdrew because of a collapsed lung.
"Alex is the fifth man in this boat, ever since Henley," Coode said. "He has encouraged us all the way and he is the strongest guy out of all of us."