TORONTO, July 26, 2012 (AFP) - The 33-year-old Piercy took advantage of superb scoring conditions by firing an eight-under 62 on the Hamilton Golf and Country Club course.
"I hit a lot of fairways and a lot of greens today," he said. "I was rolling the ball well, and obviously you've got to make some putts, too."
Piercy, who started on the 10th tee, eagled the par-five 17th and 4th holes on the rain-softened course in the first round which included a 20-minute weather delay. He also had five birdies and one bogey early in his round.
England's Owen and William McGirt, of the United States, were a stroke back at seven-under 63 and Robert Garrigus shot a 64.
Venezuela's Jhonattan Vegas, Aussie Stuart Appleby, South Africa's Charl Schwartzel, Gavin Coles of Australia and Fiji's Vijay Singh were part of a group of seven golfers at 65.
British Open champ Ernie Els, who won his fourth major on Sunday at Royal Lytham & St. Annes, opened with a two-over 72, leaving him 10 off the pace.
Piercy, of Las Vegas, collected his first PGA Tour victory at the Reno-Tahoe Open last year and he is off to a good start this season. He finished third two weeks ago at the John Deere Classic and also tied for fifth four months ago at The Transitions Championship.
"Overall it's been really solid," Piercy said, admitting that "definitely a couple weeks ago I needed to work on my wedge game," but he "kind of figured that out and produced at John Deere."
Piercy parred his opening three holes before draining a 14-foot putt for a birdie at the 13th.
At the par-five 17th, he drained a 17-foot eagle putt to reach three-under par on his round.
Five holes later he took advantage of the only other par-five. Piercy hit his second shot to 12 feet of the cup and drained his eagle putt to get to five-under par.
Piercy needed a birdie on the par-four ninth to break the course record and grab sole possession of the lead. He hit an approach shot inside 10 feet and rolled in the birdie putt for a 62 and the record.
Owen also had an eagle to go with eight birdies, a double bogey and a bogey for his 63.
He had the battle through the pain barrier after injuring his hand a week ago at the Open Championship.
"I wasn't even sure whether I would be playing this week," said Owen. "Obviously when I started that way, I'm like, okay, well, not a lot lost because I wasn't sure I would play anyway. But I started playing well and just keep moving, just keep momentum going and that's the way it was going."
Adam Hadwin, 23, was the top Canadian with a 66 in the event which also serves as the national championship.
Canadian golfing icon Mike Weir, a former Masters champion, hit a 72, and was tied for 112th with Els.
Jim Furyk, a Canadian Open winner in 2006 and 2007, shot 70.
Leading first-round scores on Thursday in the PGA Tour's $5.2 million Canadian Open (USA unless noted, par-70):
62 - Scott Piercy
63 - William McGirt, Greg Owen (ENG)
64 - Robert Garrigus
65 - Stuart Appleby (AUS), Gavin Coles (AUS), Troy Matteson, Charl Schwartzel (RSA), Vijay Singh (FIJ), Bo Van Pelt, Jhonattan Vegas (VEN)
66 - Adam Hadwin (CAN), Bill Lunde, Roland Thatcher
67 - Erik Compton, J.J. Henry, John Huh, Ryo Ishikawa (JPN), Matt Kuchar, Heath Slocum, Daniel Summerhays, Josh Teater, Cameron Tringale