Nobody can match the US star when it comes to the decathlon -- and there was no one in this field who was ever going to stop him from retaining his Olympic title.
Kevin Mayer, the young French pretender, had toyed with the idea of overhauling his illustrious opponent, but such a move never came to fruition.
While Eaton failed to reach the heights set by his own world record, his score of 8,893 points was more than enough to win and tie the Olympic record.
Mayer, who took silver with 8,834 points, edged out Canada's Damien Warner, who claimed bronze.
Eaton, 28, is the first man to retain the decathlon title since Daley Thompson in 1984.
"To win two Olympic golds in a row like Daley Thompson is very special," Eaton told reporters.
"One day, I'm going to have to meet Daley, shake his hand and thank him for giving me something to chase after.
"My throwing has been bad in the past, but I really got after the discus and shot here. Can I do three in a row? Maybe you should ask Daley."
Eaton's points total in the 10-discipline event equaled the Olympic record set by the Czech Republic's Roman Sebrle at the 2004 Athens Games.
He led from start in the two-day competition although faded slightly as Mayer closed the gap.
The Frenchman need to beat Eaton by seven seconds in the final event -- the 1,500 meters -- to take the title.
But that was never going to happen, with Eaton racing past his rival with 200 meters remaining to seal the win, clocking a time of 4:23.33 seconds.
US gold rush
Eaton was one of four American athletes to take gold in track and field events Thursday.
Dalilah Muhammad became the first American woman to win the 400-meter hurdles after she scythed through the field, clocking a time of 53.13 seconds to win by a margin of 0.42 seconds.
"The reality of winning is even better than the dream, Olympic champion, in front of my name," she told reporters.
"I put my hope and trust in my coach and it paid off. I'm so happy. I tightened over the last hurdle, but I got it done. I'm so so happy and proud."
Denmark's Sara Petersen won the silver medal ahead of Ashley Spencer of the United States.
Her male counterpart, Kerron Clement, won his hurdles race during the morning session, earning a gold medal to put in a spot in his trophy case where a note now sits reserving the space for his Rio hardware.
"It was on a piece of paper, I wrote it in January of 2016. I knew that I was coming here to get a gold medal, I had one plan for the entire season. To get the gold medal in Rio, and I did that," he said.
Elsewhere, Ryan Crouser broke a 28-year Olympic record to win gold for the US in the men's shot put final.
The 23-year-old threw 22.52 meters to break the record of 22.47 meters set by East German Ulf Timmermann at Seoul in 1988.
Crouser beat teammate and 2015 world champion Joe Kovacs, in second place, with New Zealand's Tomas Walsh taking bronze.
In the women's javelin, Croatia's Sara Kolak set a personal best and a national record to win gold and end Barbora Spotakova's quest to become the first woman to win three consecutive Olympic titles in the event.
The Czech Republic's Spotakova had to make do with bronze, with South Africa's Sunette Viljoen claiming silver.