Stuard, who began the day five shots off the lead, returned an error-free six-under 66 at the Napa Valley Silverado Resort to move into contention alongside fellow American Hahn, with a bogey-free 67 and Percy with a 68 all on 16-under 200 after three rounds.
For 46-year-old Percy, Sunday represents one more chance at clinching a first PGA Tour title which would see him realize a lifelong dream of securing an invitation to the Masters.
“It would mean the world to me. It would be fantastic,” said Percy. “It would mean I get to go to Augusta, which is a goal. I’ve never been to Augusta, which is the biggest goal you have when you come over here.
“I just thought I’d get there, I haven’t got there yet, so it’s a big deal.”
The first event of the new season looks set for a wild finish with Americans Sam Burns (72) and Harry Higgs (70), and Norwegian Kristoffer Ventura (66) all one shot back.
The final round will start with 17 players all within three shots of the lead, including 2009 British Open champion Stewart Cink.
For the second straight day Phil Mickelson carded a bogey-free round returning a two-under 70 but failed to make a dent on the leaderboard, sitting eight back of the leaders.
“This is the worst I’ve played in the last three months,” lamented Mickelson ahead of next week’s U.S. Open, where he has finished runner-up six times but never won. “It’s deceptive because I didn’t make a bogey, but I didn’t drive it well, I didn’t chip it well and I didn’t putt well.
“I turned a 64 into a 70 and I’ve got some work to do.” Reporting by Steve Keating in Toronto. Editing by William Mallard