Michael Jamieson won Great Britain's second medal in the pool when he was second in the 200 metres breaststroke after a final length shoot-out with Daniel Gyurta which forced the Hungarian to a new world record.
The 23-year-old Scot had lowered the British record twice en route to the final to become the eighth fastest swimmer in the event in history.
The Glasgow-born swimmer said earlier this year he believed a time of around two minutes and eight seconds would be required to win a medal.
Third at the final turn, Jamieson and Gyurta went head to head over the last 50m with the Athens silver medallist lowering Christian Sprenger's world mark by 0.03secs to two minutes 07.28.
Jamieson clocked 2mins 07.43secs - the third fastest time in history.
Jamieson told BBC Sport: "I am so delighted. I knew I had a little bit more to give. It's so much easier with the crowd behind you.
"I've had so many messages it has been unbelievable. I was desperate to get on the podium to repay them.
"I know how strong his last 50 is. I tried to stay on his shoulder for the first 100. I just gave everything for the last 50."
Bath ITC team-mate Andrew Willis was eighth in 2:09.44.
Gyurta's victory put paid to Kosuke Kitajima's hopes of becoming the first male swimmer ever to win the same event at three consecutive Games, the Japanese athlete won the breaststroke double at both Athens and Beijing.
However, he was fourth tonight and the only man who can now achieve the feat is Michael Phelps who can secure three consecutive 100m butterfly titles.
Kitajima's countryman Ryo Tateishi was third in 2:08.29.
Asked if someone had told him he would do this last week, Jamieson said: "I don't know if I'd have believed them to be honest.
"I knew I had a bit left after last night, I ran out of pool space a bit at the end there but I'm absolutely delighted with the silver."
Willis had set a new personal best and English record of 2:08.47 in yesterday's semi-finals.
He said: "I would like to have gone quicker but it was a great experience just being in the race."
The 21-year-old paid tribute to his team-mate with whom he trains under Dave McNulty, saying: "Michael deserves it, I'm really happy for him. He's capable of great things and we've seen that today."
Fran Halsall was fifth fastest qualifier for tomorrow night's 100m freestyle final.
The 22-year-old had been distinctly unimpressed by her performance in the heats but 53.77 this evening saw her through.
Dutchwoman Ranomi Kromowidjojo was fastest in a new Olympic record of 53.05 and with her form this year she is the clear favourite to add the title to her world bronze medal.