"When you're first alternate it's not a whole lot of fun, that feeling of only missing getting in the event by a spot, by one person," said Lashley.
"We'll see how it goes tomorrow. Hopefully I can go out there and play like today, play relaxed golf and have some fun."
Lashley, who earned his PGA Tour card for the first time in 2018, went out early and made four birdies on the front nine and finished in style with five birdies over the final six holes.
That was enough to leave him one shot clear of compatriots Ryan Armour and Nick Watney. A group of seven that included Charles Howell III and Stewart Cink were a further shot back.
"Obviously I made a lot of putts," said Lashley. "I putted well, I drove it pretty well. I hit it really well on the back nine, but at nine-under you're kind of doing everything well."
U.S. Open champion Gary Woodland, in his first event since picking up his maiden major title, mixed six bogeys with five birdies en route to a one-over-par 73 that left him 10 back of the first-round leader.
Among the other notables in the field were twice Masters winner Bubba Watson and world number 14 Rickie Fowler, who were five shots back of the leader after matching 68's.
World number two Dustin Johnson, the highest-ranked player in the field, had a roller-coaster start to his round and was two-over through 11 holes but managed three birdies the rest of the way for a one-under-par 71.
(Reporting by Frank Pingue in Toronto; Editing by Ian Ransom)
