Germany's Leo Neugebauer leads the decathlon and is well-placed to unseat reigning champion Damian Warner after three of 10 events at the Paris Olympics on Friday.
The 24-year-old Neugebauer leads with 2 876 points after excellent long jump and shot put events, while Warner has 2 798 points and Auden Owens-Delerme of Puerto Rico is with 2 786.
Canada's Warner clocked the fastest time of the morning in the men's 100 metres of 10.25 seconds to kick off the event, but Neugebauer passed the veteran with his 7.98 metres in the long jump – second best overall – while Warner's jump of 7.79 was well off his best of 8.28.
Neugebauer extended his lead with his 16.55 metres throw in the shot put, while Warner, who competed with his right hand bandaged, could muster just 14.45, more than a metre off his career best.
The biggest cheer of the event in a full Stade de France was for France's Makenson Gletty after his huge throw of 16.64 in the shot put that topped the discipline.
Neugebauer holds the world's best mark this season of 8961 points that he recorded in winning the NCAA Championships for the University of Texas. The mark put Neugebauer sixth on the all-time world best list.
Warner's best ever is the 9 018 points he scored to win the Tokyo Olympics.
The 34-year-old Canadian is the oldest in the competition, and his gold three years ago in Tokyo already made him the oldest ever to win an Olympic decathlon title.
Day one concludes with the high jump and 400 metres. Day two has the 110m hurdles, discus, pole vault, javelin and the 1 500m.
The event is missing Warner's Canadian teammate and reigning world champion Pierce LePage, who withdrew less than two weeks ago with a back injury that he said will require surgery, and France's world record-holder Kevin Mayer, who suffered a thigh injury last month.