Martin Flores carded back-to-back 66s to move a stroke clear after the second round of the RBC Canadian Open.
World number one Dustin Johnson and four other players shared the lead at the end of the first round, which was suspended by rain, but Flores climbed to the top of the leaderboard at 12 under on Friday.
Flores was flawless as he went six under, holing four birdies and an eagle at Glen Abbey Golf Course in Oakville, Ontario.
The American - seeking his maiden PGA Tour title - eagled the par-five second hole before picking up birdies at the 12th, 16th, 17th and 18th to lead Matt Every, Gary Woodland and Brandon Hagy.
Every and Hagy were tied for the lead following Thursday's rain-hit round, and both posted 68s.
Woodland starred on day two as he shot a nine-under-par 63 to improve 68 positions.
The 33-year-old - without a win since the 2013 Reno-Tahoe Open - holed 10 birdies and a bogey to surge into contention ahead of the weekend.
Vijay Singh (68), Kevin Chappell (69), Ryan Ruffels (67), Charley Hoffman (66) and Harold Varner III (65) are a shot further back.
American star Johnson is four strokes off the pace following his second-round 69, a shot behind defending champion Jhonattan Vegas (69).
A two-time runner-up at the event, Johnson was on track for a bogey-free round until he dropped a shot at his penultimate hole to be alongside the likes of Ian Poulter (69) and Keegan Bradley (69).
Bubba Watson (73) and Matt Kuchar (68) are tied for 46th at five under.