David Carry finished seventh in the Olympic 400 metres freestyle swimming event at the Aquatics Centre in which China's Sun Yang took gold.
Scot Carry touched in 3:48.62 in a race which Sun threatened to take down Paul Biedermann's world record.
At 30, Carry is the veteran of the British swimming team and he only qualified at the second trials in Sheffield last month.
Carry, who will marry world open water champion Keri-anne Payne in the autumn, said: "Walking out to that poolside, it was just about the biggest dream come true.
"And going out there in lane eight with that enormous crowd just put the biggest smile on my face.
"It was just completely amazing. That soon changed as soon as I started swimming, because I was absolutely hurting after that swim that I had to do this morning to get into the final.
"It was hurting from the start but that crowd just pulled me along and to come seventh in the world, with this home support, in these Olympics, I really can't ask for better than that.
"We've got the 4x200 freestyle relay on Tuesday, so I've got a feeling we're going to do a pretty good job there."