Rio de Janeiro - USA star Ashton Eaton will head into the second day of the Olympic decathlon with a 121-point lead over Germany's Kai Kazmirek.
Canadian Damian Warner, reigning world silver medallist, sat in third, 132 points adrift of Eaton, the reigning Olympic and world champion.
Eaton amassed 4 621 points from Wednesday's opening day of action.
The 28-year-old American timed 10.46 over the 100m, went out to 7.84m in the long jump, managed bests of 14.74m in the shot put and 2.01m in the high jump, before rounding off a gruelling first day in scorching temperatures with 46.07 in the 400m.
"I feel OK about day one," said Eaton.
"It's just going through the motions, nice and smooth.
"The whole thing is going smooth, I guess, nothing really outstanding."
Eaton added: "I did actually like my shot put. In the first throw, that was awesome for me to throw 14.70.
"I think maybe one of my furthest in this series."
Kazmirek leapfrogged Warner into second after clocking 46.75 in the 400m.
But Warner insisted nothing was over going into the second day of the gruelling 10-discipline event.
"It wasn't terrible, but I know that there was so much more that I could have gained," Warner said.
"It's up to me now tomorrow. I was expecting to come out here and score a lot of points on day one and that didn't happen.
"Day two is something that I always look forward to because I know that I am very strong in a lot of those events. I'm looking forward to tomorrow."
Eaton, however, remains the overwhelming favourite, unbeaten in combined events competition since the 2011 world championships in Daegu.
Since his triumph in London in 2012, Eaton has won four more world titles - two indoors and two outdoors - and has upped his decathlon world record to 9 045 points with his scintillating victory at last year's Beijing world championships.
The decathletes tackle the 110m hurdles, discus, pole vault, javelin and 1 500m on Thursday.
Not among them will be Germany's world bronze medallist Rico Freimuth, who pulled out after the first three events.