Eaton deservedly took the unofficial title of the world's greatest athlete when he won gold in the Olympic decathlon on Thursday with a total of 8,869 points.
World champion Trey Hardee took silver, 198 points behind in a United States one-two and Cuba's Leonel Suarez secured a second successive bronze thanks to an Olympic best performance for the decathlon of 76.94 metres in the javelin.
Eaton had virtually sealed the gold medal after nine of the 10 events but after dragging himself around the concluding 1,500 metres in a time of four minutes 33.59 their was only relief on his face.
The 24-year-old had a cushion of 222 points going into the race and was content to stay in the pack, not bothering to follow when Belgian Hans van Alphen upped the pace.
Eaton caught his breath and was congratulated by the other decathletes. They then started the customary joint celebrations, posing for a group photo before setting off on a lap of honour.
Having broken Roman Sebrle's 11-year-old world record in June, Eaton missed out on taking the Czech's Olympic mark of 8,893 by 24 points.
He had started the second day with a lead of 220, only to be pegged back to 99 points by Hardee after a poor discus. However, Eaton took control again with third place in the pole vault of 5.20 metres and a personal best of 61.96 in the javelin.
He was helped in the pole vault by the failure of Hardee's gamble of passing at 4.90 and going straight to 5.00.
Wearing a support on his right elbow following surgery last year, Hardee knocked the bar off on all three attempts, leaving him with a best of 4.80 and allowing Eaton to stretch his lead.
He had been left shaking his head at the end of the discus after only managing 42.53, almost five metres down on his personal best for 22nd out of the 27 athletes.
Hardee, the stronger thrower of the U.S. pair, had finished third in the discus with 48.26 for 834 points, 118 more than Eaton's mark earned, to close the gap on the leader.
"I threw a terrible one, he threw a bad one and I was like 'all right, we're doing okay'," Eaton told reporters.
"I threw another bad one, he threw an awesome one and it was: 'oh I have to figure out what I'm doing and do this' and I threw another bad one. I was so disappointed with myself... he competed well. I didn't."
Hardee also beat Eaton in the day's first event, the 110 hurdles, shouting as he crossed the line in a personal best time of 13.54.
Eaton had got his first Games off to a flying start on Wednesday with the fastest 100 metres in an Olympic decathlon of 10.35 seconds. He then won the long jump with 8.03 metres before going close to his personal best in the shot put with 14.66.