Ashton Eaton won the decathlon gold medal as he finished 198 points ahead of United States team-mate Trey Hardee with 8,869 points.
Eaton held a 151-point lead after nine events and the 24-year-old finished seven seconds ahead of world champion Hardee in the closing 1,500 metres.
Cuba's Leonel Suarez produced a season's best of 8,523 to claim bronze.
Eaton led from the first event after recording the fastest ever 100m - 10.35 seconds - in an Olympic decathlon.
The Texan, who set a new
world decathlon record at the US trials in June,
finished just 24 points short of Romain Sebrle's Olympic decathlon record of 8,893 points.
Czech Sebrle, who set the record on his way to gold at the Athens Games,
pulled out of the decathlon
after aggravating a heel injury in the 100m.
Eaton started the second day of events on Thursday with a strong 110m hurdles but lost ground in the discus, finishing 16th overall, before clearing 5.20m in the pole vault to extend his lead once more.
Hardee threw 66.65m in the javelin to keep the pressure on his rival but Eaton is a better middle distance runner and finished seven seconds clear of his team-mate to clinch gold.
Eaton had amassed 4,661 points and a 220-point lead over Hardee at the halfway stage after solid performances in the 100m, long jump, shot put, high jump and 400m.
He jumped furthest in the long jump with a leap of 8.03m but threw 14.66m in the shot put to finish 10th in that discipline.
Eaton extended his lead in the evening, clearing 2.05m in the high jump, before setting the fastest 400m time with a run of 46.90 secs.
Britain's Daniel Awde was forced to withdraw with a knee injury.