Fifteen-year-old Josef Craig claimed gold in the S7 400 metres freestyle, breaking his own world record in the process.
Craig swam four minutes 42.81 seconds to beat the mark of 4mins 45.79 secs he set in the morning's heat, winning by 3.41 seconds from China's Pan Shiyun.
Moments later Susie Rodgers took bronze in the women's equivalent to claim Great Britain's 100th medal of the Games.
Craig told Channel 4: "I genuinely didn't think this would happen but I thought 'last 400m of the season, it doesn't matter if I die at the end, just go for it, it doesn't matter.
"I didn't realise that I'd broken the world record, I didn't think I had it in me. But obviously because of this great crowd again and all this support, I managed to.
"It means more than anything in the world. It's the happiest day of my life. I can't believe what's happened. It's amazing. I wish I could do it all over again."
Jacqueline Freney picked up her seventh title of London 2012 in the women's race, destroying the rest of the field.
Rodgers battled with American Cortney Jordan, edged out by 0.38secs in 5:18.93.
Steph Millward was second behind Natalie du Toit as the South African won her third consecutive title in the SM9 200m individual medley with Louise Watkin in third.
Millward touched in 2:36.21 ahead of Watkin, who picked up her second silver in 24 hours, in 2:37.79 as she overhauled team-mate Claire Cashmore in the final 15m.