TORONTO, 25 July 2015 (AFP) - The American, in search of a fifth career title and his first since 2007, had a 36-hole total of 14-under par 130 and was two strokes clear of compatriot Brian Harman, who carded a 67 for 132.
"Never really felt like it was going to be a crazy round, which nine birdies -- I'm definitely happy with it," said Campbell, whose round was one stroke shy of the Glen Abbey record when played at par-72 -- posted by Greg Norman in 1986 and John Merrick in 2013.
Campbell birdied all four of the course's par-fives. Although he has hit just 14 of 28 greens in regulation in the first two rounds, he needed only 25 putts on Thursday and 24 on Friday.
"It's kind of weird because it happened with the par-fives," said Campbell, a former US Ryder Cup player. "Knocking them on in tow and two-putting. I made a couple of long putts, which always helps."
Canada's David Hearn fired a 64 to share third place on 133 with American Johnson Wagner, who posted a 66.
If he can pull off the victory in his home open Hearn would become the second Canadian to win on tour this season, after Nick Taylor's triumph in Jackson, Mississippi, back in November.
The last Canadian to win the Canadian Open was Pat Fletcher in 1954.
"If I continue to keep playing the way I am, I know I have a chance," said Hearn, who had eight birdies in his bogey-free effort. "I can't control what Chad or any of the other players are going to do. But if I keep doing what I'm doing and stay focused on that, I like my chances."
Australian Jason Day, coming off a share of fourth place at the British Open at St. Andrews, was alone in fifth place on 134 after a 66.
The world number 10 highlighted his round with an eagle at the par-five 18th.
Although the weather-induced Monday finish at St. Andrews left Day with a short turnaround, he didn't think fatigue would be a factor at the weekend.
"I'm driving it great," Day said. "I'd like to tune up the iron shots, but overall I'm hitting it good.
"Biggest thing for me is still trying to get as much rest as possible, especially coming off last week so that I can stay mentally sharp."
Leading second-round scores on Friday in the USPGA Tour's Canadian Open (USA unless noted, par-72, a-amateur):
130 - Chad Campbell 67-63
132 - Brian Harman 65-67
133 - David Hearn (CAN) 69-64, Johnson Wagner 67-66
134 - Jason Day (AUS) 68-66
135 - Erik Compton 66-69, Eric Axley 67-68, Bubba Watson 68-67
136 - Michael Putnam 71-65, Brooks Koepka 68-68, Chez Reavie 69-67, Scott Pinckney 68-68, Vaughn Taylor 65-71, William McGirt 67-69, Emiliano Grillo (ARG) 64-72
137 - Colt Knost 68-69, Andres Gonzales 70-67, Brendon de Jonge (ZIM) 71-66, Alex Prugh 67-70, Jim Furyk 68-69, Charley Hoffman 71-66
138 - Mark Wilson 70-68, Justin Leonard 72-66, a-Austin Connelly 73-65, Austin Cook 68-70, Steve Wheatcroft 66-72, Ricky Barnes 68-70, Pat Perez 69-69, Matt Kuchar 69-69, Camilo Villegas (COL) 69-69, Jonas Blixt (SWE) 69-69, Lucas Glover 70-68