Dustin Johnson and Luke List have taken a share of the lead at the Canadian Open following first-round 66s at the Glen Abbey Golf Club in Ontario.
The world number two, who won the US Open last month, hit three consecutive birdies on the front nine, but dropped a shot just before the turn.
Johnson double bogeyed the 14th hole, but he recovered with a birdie on the 16th and an eagle on the 18th, while List had an unblemished round with six birdies as both finished six-under-par.
Chesson Hadley, Kelly Kraft and Jon Rahm are one shot off the pace, and they are joined by Canadian amateur Jared du Toit, who carded five-under-par 67.
The inexperienced golfer shot five birdies, one bogey and an eagle on the 17th hole.