Joel Dahmen fired a 10-under 62 to grab a 2- stroke lead at the Cape Breton Celtic Classic before play was suspended due to darkness.
Dahmen, who has a pair of top-10 finishes this season, is seeking his first career win on the PGA Tour Canada.
Wes Homan shot an 8-under 64 to sit alone in second place, while Times Colonist Island Savings Open winner Stephen Gangluff owns third at 6-under 66.
David Skinns, Micah Burke and Ryan Blaum shared fourth at 5-under 67.
Twenty-nine players will need to finish their opening round when play resumes on Friday.
Dahmen opened his round with back-to-back birdies at the first and second, and later poured in four birdies over a five-hole stretch from the sixth to move to 6-under.
After tripping to a bogey at the 11th, he regained his early form by racing into the clubhouse with five birdies over his final six holes to move to the top of the leaderboard.
Homan had earlier grabbed the clubhouse lead by recording eight birdies during his bogey-free round.
NOTES: Johnny Bloomfield hit a hole-in-one at the 15th hole ... This is the second straight new event on the PGA Tour Canada ... This is the first time the PGA Tour Canada has played on the east coast since the 2001 Aliant Cup in St. John's, Newfoundland.