Atwal, who exited after the first event of the four-week Fedex Cup play-off, started sedately with a series of eight pars before an eagle on the par-five ninth set him off at TPC Summerlin.
He then birdied the 13th, 14th and 18th for a flawless 66.
Jhonattan Vegas and William McGirt carded career-best eight-under 63 each to take a share of the lead in the first round.
Rookie Vegas of Venezuela, who broke through for a win in Bob Hope Classic earlier this season, sank 10 birdies against two bogeys.
McGirt, also a rookie, had a bogey-free round with eight birdies in one of the last groups of the day. Both Vegas and McGirt were leading in a PGA Tour event for the first time.
Justin Timberlake Shriners Hospitals for Children Open is the first of the four events in the Fall Series.
Nathan Green and Charlie Wi with 64 each were tied third and there were 11 players, including Nick Watney, at 65, followed by another 12 at 66.
