Imada, a former University of Georgia player, and Matteson, a former Georgia Tech star, had 13-under 203 totals. Villegas was 11 under after a 68, and Masters champion Zach Johnson (69), local favorite Matt Kuchar (64) and Lee Janzen (67) were 10 under.
Imada nearly eagled the par-5 18th despite flying the rear bunker. He tapped in after chipping within a foot of the hole, a shot that caused many in the gallery to bark in approval at the former Georgia Bulldogs standout.
Matteson had a two-stroke lead over his partner after a birdie at the par-4 14th, but Imada set up his spectacular finish with a birdie at the par-3 16th.
Villegas, a 25-year-old Colombian, moved into a share of the lead with three straight birdies before bogeying No. 8.
Matteson closed last season with five straight top-10 finishes, including his first career victory, but he arrived this week having missed six cuts in his last eight events.
Janzen hasn't won since earning his second U.S. Open title in 1998.
Matteson was helping Janzen lobby AT&T tournament director Dave Kaplan for a sponsor's exemption before so many of the PGA TOUR's top players declined invitations. That allowed Janzen, who didn't qualify the last three weeks, to join the field.
'As of last week, I wasn't in the field yet, but I had made reservations at a hotel and planned on coming all along,' Janzen said. 'I've played this tournament every year since we moved to the new course.'
Kuchar's 64 was the best round of the day.
A victory in suburban Atlanta would mean a lot to Kuchar, who still has a home in the metro area after starring at Georgia Tech. After winning the 1997 U.S. Amateur, Kuchar burst upon the golf scene at the '98 Masters, where he flashed an infectious smile and finished in the top 25 at Augusta National to become a gallery favorite.
Since winning the 2002 Honda Classic, however, Kuchar struggled so much that he lost his card before finishing in the top 10 of the Nationwide Tour money list last year.
'On the golf course, it's easy to beat yourself up,' Kuchar said. 'You just have so many more bad things happen than good ... it seems. Just to get a win every 100 tournaments would be great. You just don't get that much success out here.'