Brad Adamonis posted a 5-under 67 to finish four shots off the pace at 13-under-par 203 alongside Brent Winston, Jeff Freeman and Marco Dawson.
Gore, who captured the 2000 New Mexico Classic, jumped out of the gate Saturday with two birdies over his first three holes at Shadow Hills Country Club. He added another birdie at the par-4 sixth to make the turn at minus-13.
The 28-year-old continued the barrage on the inward nine with back-to-back birdies starting at the 10th to take the lead outright. Gore kept his challengers at bay with a birdie at the 15th and further distanced himself from the pack with a birdie at the par-5 last.
'I played solid today,' said the former Pepperdine University star. 'I didn't hit it perfectly, but when I didn't I made some good putts to save it and made some good chip shots. That's what you have to do, keep your head in there and keep plugging. You have to be patient out here, but most importantly you have to miss it on the right side.'
Gore, who turned pro in 1997, earned his PGA Tour card in 2001 after finishing tied for 14th at the 2000 PGA Tour Qualifying School. His best finish on the main circuit was a tie for 18th at the 2001 Invensys Classic at Las Vegas.
'I've been here before, but just not as often as I like,' said Gore, who established a new 54-hole tournament record. 'There's four rounds in a golf tournament so I did my job today. If I play my best, that's all I can do. Winning is a by-product of how you control your emotions and your game. That's my goal, to try and go out and make some birdies.'
Imada opened with an eagle at the par-4 second to go along with two birdies on the front side to make the turn at 13-under. The 25-year-old, who won the 2000 Virginia Beach Open, added two birdies on the back side for a round of 66.
'I haven't really been playing well this year, so I don't have anything to lose,' said Imada. 'I'm going to go out there and try to have fun. I haven't been in this position since last year. It's just nice to be back.'
Tjaart van de Walt shot a 5-under 67 to finish alone in seventh at 12-under-par 204. The South African was followed by Trevor Dodds, Jason Dufner and Patrick Moore, who are knotted at 11-under-par 205.
Overnight leader Ted Purdy struggled to hold his lead and fell apart with a double bogey at the par-4 14th. Purdy found more trouble with a double bogey at the par-4 17th en route to a 74. The 29-year-old is part of a group at 10-under-par 206.
Full-field scores from Oregon Classic