Atwal, who last year became the first Indian to win on PGA Tour, sank three birdies against two bogeys at the Colonial Country Club here.
American David Toms carded a bogey-free eight-under 62 to share the first-round lead with fellow countrymate Chez Reavie.
Toms last week lost the playoff to KJ Choi at The Players Championship.It was Toms' best score in 429 rounds -- since a career-best 61 at the Sony Open in Hawaii in January 2006. That was the last of his 12 PGA Tour victories.
Rickie Fowler shot a 63, missing a chance to tie the tournament record after his approach on his final hole, the 407-yard Number 9, hit the green and spun back into the water.
He closed with a double-bogey six in a round that included an eagle, eight birdies and a three-putt bogey from 6 feet at the par-3 16th.
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