Graeme McDowell had a day to forget at the RBC Canadian Open in Oakville.

An early gain on the second was quickly overshadowed by six bogeys over the course of his opening round, before the former US Open champion stopped the rot with a birdie four on the 18th for a score of four-over 76.

Brendan Steele was the unlikely figure at the top of the leaderboard after the opening day's play at the Ontario venue.

The American made the most of clear conditions at Glen Abbey Golf Course by sinking eight birdies in a round of 65, his only blemish coming on the par-four ninth - his final hole of the day.

That left Steele with a slender lead over compatriots Scott Brown and Matt Kuchar as well as Australian Scott Gardiner.

And the 30-year-old Californian, without a win since his maiden title at the 2011 Texas Open and with just one top-10 finish this season, seemed satisfied with his day's work.

"Overall, it was a good day," Steele said on "I hit a lot of good shots and was able to hole a lot of putts.

"I also didn't miss many greens or hit many shots off-line and I was able to roll a few putts in."

Brown enjoyed a bogey-free round of six-under 66 while the highlight on Kuchar's card was an eagle on the par-five 18th.

Gardiner sank six birdies in a row between the second and seventh holes, adding another on the 15th before bogeying the next.

Sweden's David Lingmerth was the leading European on five under, sitting alongside Hunter Mahan on the leaderboard, but it was a topsy-turvy and ultimately disappointing day for England's Luke Donald.

The 35-year-old former world number one, who missed the cut at last weekend's Open Championship, began his round with a dropped shot before making birdies on the fifth and seventh.

However, that was followed by bogeys on the ninth and 12th and a double bogey on the par-four 14th, although he undid some of the damage by picking up two shots in the last three holes to finish one over.