Hunter Mahan fired an 8-under 64 on Friday to move two strokes clear of the field after two rounds of the Canadian Open.
Mahan, who has been in the final group at the last two majors, ended 36 holes at 13-under-par 131.
John Merrick fired a 10-under 62 to soar into second place at minus-11. Bubba Watson is alone in third at 9-under 135 after a second-round 67.
Aaron Baddeley and Patrick Reed have both posted back-to-back 68s and they share fourth at 8-under 136. Tommy Gainey carded a 64 to climb into a share sixth at minus-7. He was joined there by James Hahn (68) and Chris Kirk (69).
First-round leader Brendan Steele struggled to a 3-over 75 and tumbled into a tie for 26th at 4-under 140 at Glen Abbey Golf Club.
Mahan was six back of Merrick at the start of his second round as Merrick played in the morning wave. Mahan 2-putted for birdie at the par-5 second and followed with birdies at three and four to move to 8-under.
The 31-year-old cruised to six consecutive pars from the fifth. Mahan stuffed his approach inside two feet at the 11th and kicked that in for birdie.
Mahan found the green in two at the par-5 13th and 2-putted for birdie to get within one of Merrick. Three holes later, Mahan chipped his third to six feet and converted that to join Merrick at minus-11.
At the 17th, Mahan rolled in a 4-footer for birdie to move one clear. He drained a 13-footer for birdie at the last to finish two ahead of Merrick.
"I just played free. That's how I think I was able to birdie the last three, because I just kind of kept my head up and kept going," said Mahan, who has been on the five of the last six Presidents or Ryder Cup teams. "I wasn't really thinking about finishing strong or anything, I was just trying to finish that hole and stay in the present as much as I could and not get too caught up in the leaderboard or anything else."
Merrick, who won at Riviera earlier this year, holed an eagle chip from over the green at the second, then parred four in a row. He kicked off a stretch of eight birdies in the final 12 holes at the seventh, where he made an 8-footer for birdie.
He made it two in a row as he poured in a 32-footer for birdie at eight. Merrick kicked in a short birdie effort at 10 and again made it two in a row as he ran home a 34-footer for birdie at 11.
Merrick dropped his third at the par-5 13th to four feet and converted that for birdie. He moved to 6-under with a birdie at 15. Merrick closed with birdies at 17 and 18 to enter the clubhouse with the lead at minus-11.
"I wasn't hitting it that great on the range and I didn't feel that good. Maybe that makes you focus a little bit more, try to figure out what's going on, and I was able to kind of work a couple things out," Merrick admitted. "I got off to a good start, hit it over the green on two and chipped in for eagle. My game has been feeling pretty good lately. Everything kind of clicked today."
NOTES: Merrick's 62 matched the course record at Glen Abbey ... Charl Schwartzel carded a double-eagle on the par-5 second at Glen Abbey as he holed a 9-iron from 176 yards out ... Defending champion Scott Piercy made the cut as he carded back-to-back 71s to end two rounds at minus-2 ... With 79 players making the cut, that means there will be a second cut after the third round to the closest number to 70 after 54 holes ... Of the 18 Canadians that started the event, only four -- Mike Weir, Brad Fritsch, Roger Sloan and David Hearn -- made the cut ... The cut line fell at 1-under 143 with 79 players moving on to the weekend ... Among those that missed the cut were Luke Donald, Ricky Barnes, John Rollins, Geoff Ogilvy and last week's Sanderson Farms winner Woody Austin.