Weir, using the tournament as a competitive tool to regain his professional edge in the wake of elbow surgery, is six shots back.
"I'm not very sharp, that's the biggest thing," said Weir, who finished with five birdies, three bogeys and a handful of scrambling par saves.
The chip-and-putt to save par was the most successful part of Weir's game. Too often, he found the rough off the tee.
"Probably on the whole, I'm discouraged," the Sandy resident said. "I've been striking the ball a little better than that."
Meanwhile, Tony Finau used Weir's surprise entry into the tournament as motivation.
"It's great for the tournament," said Finau, who finished with eight birdies and a bogey. "It's great for all of us to play against one of the best players in the world, and at one time was the best player in the world.
"It's a great opportunity to compete against a guy like that and measure ourselves."
One consistency throughout the first day was how the bulk of the low scores came during the morning round, when the greens were receptive before drying out in the 90-degree heat and spike marks made putting more difficult.
Defending champion Clay Ogden of Farmington played the afternoon round and finished at 2-under.
"The course seems to dry out really fast," said Brown, who finished second last year. "In the morning, balls are easier to stop than in the afternoon."
Brown used the receptive greens to make five straight birdies on the front nine and an eagle on the par-5 16th. And it still could have been better.
"It's weird," he said. "You can shoot 63 and still think you left three or four shots out there. Until you shoot in the 50s, you always feel like you can shoot lower. I'll take a 64."
P At Oakridge Country Club (Farmington)
Saturday's key tee times:
• Clay Ogden, 8:50 a.m.
• Derek Tolan, 1:40 p.m.
• Mike Weir, Tony Finau, 1:50 p.m.
• Zenon Brown,2:10 p.m.
Derek Tolan -8
Zenon Brown -8
Dusty Fielding -7
Tony Finau -7
Gipper Finau -7
Zac Blair -5
Mike Weir -2
Clay Ogden -2
Boyd Summerhays -1