Emiliano Grillo fired an 8-under 64 in Thursday's first round and he grabbed a 1-shot lead at the Canadian Open.
Grillo, who spends most of his time playing on the European Tour, has never won on the PGA Tour. He qualified to play in this event by finishing tied for 10th at last week's Barbasol Championship.
Brian Harman and Vaughn Taylor carded matching 7-under 65s at Glen Abbey Golf Club and they share second place.
Erik Compton, Steve Wheatcroft, Tyrone Van Aswegen and amateur Ryan Ruffels are one shot further back and tied for fourth following 6-under 66s.
Defending champion Tim Clark carded an even-par 72, putting him in a tie for 88th and eight shots back.