Damian Warner leads the field with 4,531 points after Day 1 at the Hypo Meeting in Götzis, Austria.
Warner, who won gold in the decathlon at the 2020 Olympic Games, was making his return to competition after 10 months of rehabilitation following a hamstring injury.
He suffered the injury at the end of last year’s world championships and missed the Commonwealth Games.
Warner has won the Hypo Meeting a record seven times and each of the previous six.
Fellow Canadian Pierce LePage is in second with 4,513 points.
The competition’s final round on Sunday begins with the 110-metre hurdles, followed by discus, pole vault, javelin and the 1,500 metres.