Matthew Centrowitz produced a stunning gun-to-tape 1500m run on Saturday to claim the United States' first gold in the event since 1908.
Algerian defending champion Taoufik Makhloufi added silver to second place in the 800m, in 3:50.11, while New Zealand's Nicholas Willis claimed bronze (3:50.24).
The last American to win the 1500m in the Olympics was Mel Sheppard in the 1908 london Games, and Centrowitz was left shell-shocked by his performance.
"It hasn't sunk in yet. I had an email from Jim Ryan before the race, Seb Coe gave me the medal and Hicham El Guerrouj is back there," he said in reference to the US 1968 1500m silver medallist, IAAF president and two-time Olympic gold medallist in the event and the Moroccan world record holder respectively.
"Seb said: Welcome to the club!
"Everything leading up to it, during and after has been surreal. "I saw my dad on my victory lap and I yelled 'are you kidding meIJ!' and he yelled back 'are you effing kidding meIJ!' and it kept going back and forth. I don't think any of us believed it."
Centrowitz added: "There's no achievement in sport that tops Olympic gold, no world record, no other medal.
"The Olympics are the pinnacle of track and field. This is the best that it gets. I've been joking since I got this medal that I don't have to do anything else in my career! On the best day I thought I could have got silver. Coming away with gold is unbelievable," said Centrowitz.