Luke Donald and Graeme McDowell had days to forget as Brendan Steele set the early pace at the RBC Canadian Open in Oakville.
Donald missed the cut at the Open and there was no respite for the former No 1 in Ontario.
And up and down round saw him register a double bogey, three bogeys and four birdies to finish on one-over - eight shots behind Steele.
McDowell endured a torrid time, with the former US Open signing for a four-over 76 - with his round including six bogeys and two birdies.
While the Ryder Cup duo struggled at Glen Abbey Golf Course, Steele was in superb form to open up a one-shot lead over Scott Brown, Matt Kuchar and Scott Gardiner.
The 30-year-old holed eight birdies, with the sole blemish on his round coming at his final hole.
Steele, whose only Tour title came at the 2011 Texas Open, told pgatour.com: "I love being up here. I played in '06 and '07 on PGA Tour Canada. And really, got me ready to play the Nationwide Tour, which I played in '08, '09 and '10.
"It was a great progression in my life. I had a great time up here. Made a lot of friends and spent two summers traveling the country.
"Really, just an overall good day. Hit a lot of good shots and was able to hole some putts. When you have a good round like that and you play that well, you kind of have everything going.
"Today was probably the most complete round that I've had all year, so that was kind of nice. Didn't miss many greens, didn't 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.