Eaton set the decathlon world record at the U.S. trials in June and backed it up with an Olympic victory with 8,869 points.
Two-time world champion Trey Hardee settled for silver with 8,671 points and Leonel Suarez of Cuba took the bronze, 346 points behind Eaton, at 8,523.
Damian Warner of London, Ont., finished fifth with a personal best score of 8,442.
Eaton had a 151-point lead going into the final event, the 1,500 metres, and is a better middle-distance runner than Hardee. But there were still some nerves in the field, with a rare false start in the 1,500.
Eaton needed to slash six seconds off his fastest ever time in the 1,500 to break his world record, but ran a cautious race and finished well outside his personal best in 4 minutes, 33.59 seconds.
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