Matt Kuchar and Scott Brown share the Canadian Open lead, but the second round belonged to the surging Brandt Snedeker.
Snedeker shot a 10-under 60 to climb into a tie for third place at 11 under alongside Nick Taylor, a stroke adrift of Brown and Kuchar.
Snedeker's second-round score was the lowest 18 holes in tournament history at the Hamilton Golf and Country Club. He carded eight birdies and one eagle, which came on the par-five fourth hole.
The mistake-free round was also the second lowest on the PGA Tour since the start of the 2017-18 season. Snedeker, who shot a 59 at the Wyndham Championship last year, is the first player since 1983 to have one round of 59, 60 and 61 on the PGA Tour.
"I think it's my putting. When I get hot, I feel like the hole is a beach ball to me," Snedeker said after his round, via Golfweek.com. "I'm not scared about going low. I realise these days don't happen very often. So it almost gets me more excited if I feel like it's going that way."
Kuchar also fared well heading into the weekend. He had one blemish at the par-four seventh but otherwise finished with eight birdies for a seven-under 63.
Brown matched Kuchar's second round to join him in first place.
Brown, who is searching for his first win since the 2013 Puerto Rico Open, said it was due to his irons. He had an eagle on the front nine and five birdies on the back nine.
"Just a lot of good iron shots," Brown said, via GolfDigest.com. "Kind of was feeling it with the irons and had a lot of good looks for birdies most of them."
Webb Simpson sits in fifth place at 10 under, Adam Hadwin follows in sixth at nine under and Mackenzie Hughes, Henrik Stenson and Graeme McDowell, among others, make up a sizable tie for seventh a shot further back.
McDowell, at one point, was in control of the leaderboard after he fired off three birdies. But two bogeys on his back nine pushed him back down the standings.
Dustin Johnson, the 2018 champion, is in a tie for 33rd place at four under with the likes of Brooks Koepka.
Surprisingly, the world's top two were just above the two under cut line.
Some notable names not making it into the weekend were Russell Henley, J.B. Holmes and Sergio Garcia.