Anthony Painter posted a 8-under 64 to take a share of third place at 13-under-par 202. He is joined there by Tony Carolan (70). Rick Price, Brad Bryant, Richie Coughlan and Shane Bertsch are one stroke further back at minus-12.
The players battled rain throughout the round, which led officials to put lift, clean and place rules into affect for the round.
Imada began his day four shots behind overnight leaders Carolan and Brett Wetterich at the Cliffs Valley Course. He dropped in a 15-foot birdie try at the par-4 third and came right back to birdie the next from 40 feet out.
The 2000 Virginia Beach Open then birdied the two front nine par-5s, Nos. 6 and 9, to get to minus-11. Around the turn, Imada again birdied two straight holes from the 12th.
Imada capped a bogey-free round by sinking a 3-foot birdie putt at the par-4 16th to grab a share of first place.
'I drove it a little better today than I did the first two rounds,' said Imada, who hit 13-of-14 fairways and missed just one green in regulation. 'If you hit it in the fairway you can attack the pins a little more with lift, clean and place. Obviously, that makes it easier to score.'
Thompson shared fifth place entering Round 3. He opened with a birdie at the first. He dropped a shot at the fifth, his first bogey since the first hole of his second round.
The 25-year-old came right back to eagle the par-5 sixth from 25 feet out to move to minus-11. After five straight pars, Thompson dropped in a birdie putt at the par-4 12th.
Thompson kept climbing the leaderboard with a 20-foot birdie at the 15th. He came back with a two-putt birdie on No. 17 to close out his 67.
'You've got to stay real patient around a course like this,' Thompson said. 'This just shows how good juniors from this state are. I've grown up on courses like this my whole life. I know all the breaks of the greens.'
Wetterich managed just an even-par round of 72 on Saturday. He shares ninth place with Steven Alker, Bill Lunde, Bryant Odom, Euan Walters, Jason Gore and Paul Gow.
Ahmad Bateman, Jody Bellflower, Franklin Langham, Sonny Skinner, Vance Veazey, Jimmy Walker, Tyler Williamson and Brian Hull are one stroke further back at minus-10.
Thompson and his partner, George Rogers, won the celebrity Pro-Am portion of this event at 32-under-par 183 in a match of cards over Hull and his amateur playing partner, actor Kevin Costner.