Jason Bohn, Jeff Overton and Blake Adams shot 7-under 63s to share the first-round lead at the Colonial, where 2008 champion Phil Mickelson's return turned into a struggle after an impressive start Thursday.
Mickelson birdied the first two holes, but that was the lowest he got on a hot day with ideal scoring conditions. Lefty finished with a 1-over 71 and is tied for 89th place, while 75 players were under par.
It will take quite a comeback for Mickelson to win his third Colonial, a victory that would push him to No. 1 in the world ranking ahead of Tiger Woods for the first time in his career.
Mickelson wasn't at a pink-swathed "Hogan's Alley" to defend his title last May after finding out that his wife, Amy, had been diagnosed with breast cancer.
Brian Davis was alone in fourth with a 64. Defending champion Steve Stricker shot 68.