Rory McIlroy was off the pace at the Canadian Open as he carded a one-over-par 71 in the first round.
The Northern Irishman hit three birdies but four bogeys in Ontario to trail clubhouse leader Thorbjorn Olesen by 10 shots.
Dane Olesen's nine-under-par round of 61 included an eagle, eight birdies and a bogey.
McIlroy completed the career Grand Slam of winning all the majors with victory at the Masters in April.
However, he produced a disappointing showing at the US PGA in May and his struggles continued at the Canadian Open as he prepares for next week's US Open.
Elsewhere, Irishman Shane Lowry carded a promising 64 to end the first round on six under, while defending champion Robert MacIntyre, of Scotland, and England's Danny Willett were a further shot back.